Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.55   13.701%   $207.5612   $207.56   $207.55   $207.60  
  Purchase #2 $121.90   11.416%   $135.8161   $135.82   $135.80   $135.80  
  Purchase #3 $188.40   6.684%   $200.9927   $200.99   $201.00   $201.00  
  Purchase #4 $217.31   11.548%   $242.405   $242.41   $242.40   $242.40  
  Purchase #5 $167.62   7.665%   $180.4681   $180.47   $180.45   $180.50  
  Purchase #6 $122.25   9.770%   $134.1938   $134.19   $134.20   $134.20  
  Purchase #7 $168.44   7.579%   $181.2061   $181.21   $181.20   $181.20  
  7 purchase totals = $1,168.47       $1,282.6430   $1,282.65   $1,282.60   $1,282.70