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 $51.66   12.199%   $57.962   $57.96   $57.95   $58.00  
  Purchase #2 $236.85   3.135%   $244.2752   $244.28   $244.30   $244.30  
  Purchase #3 $9.78   3.209%   $10.0938   $10.09   $10.10   $10.10  
  Purchase #4 $157.29   11.719%   $175.7228   $175.72   $175.70   $175.70  
  Purchase #5 $179.39   11.360%   $199.7687   $199.77   $199.75   $199.80  
  Purchase #6 $24.77   6.641%   $26.415   $26.42   $26.40   $26.40  
  Purchase #7 $154.46   11.118%   $171.6329   $171.63   $171.65   $171.60  
  7 purchase totals = $814.20       $885.8704   $885.87   $885.85   $885.90