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 $223.87   3.631%   $231.9987   $232.00   $232.00   $232.00  
  Purchase #2 $110.43   12.140%   $123.8362   $123.84   $123.85   $123.80  
  Purchase #3 $165.58   5.481%   $174.6554   $174.66   $174.65   $174.70  
  Purchase #4 $236.90   6.157%   $251.4859   $251.49   $251.50   $251.50  
  Purchase #5 $112.53   11.580%   $125.561   $125.56   $125.55   $125.60  
  Purchase #6 $121.98   11.522%   $136.0345   $136.03   $136.05   $136.00  
  Purchase #7 $222.77   7.590%   $239.6782   $239.68   $239.70   $239.70  
  7 purchase totals = $1,194.06       $1,283.2499   $1,283.26   $1,283.30   $1,283.30