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 $165.93   13.176%   $187.7929   $187.79   $187.80   $187.80  
  Purchase #2 $199.43   11.675%   $222.7135   $222.71   $222.70   $222.70  
  Purchase #3 $98.88   7.120%   $105.9203   $105.92   $105.90   $105.90  
  Purchase #4 $118.98   3.301%   $122.9075   $122.91   $122.90   $122.90  
  Purchase #5 $39.95   3.416%   $41.3147   $41.31   $41.30   $41.30  
  Purchase #6 $143.99   10.409%   $158.9779   $158.98   $159.00   $159.00  
  Purchase #7 $228.31   3.588%   $236.5018   $236.50   $236.50   $236.50  
  7 purchase totals = $995.47       $1,076.1286   $1,076.12   $1,076.10   $1,076.10