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 $43.36   12.164%   $48.6343   $48.63   $48.65   $48.60  
  Purchase #2 $178.68   11.723%   $199.6267   $199.63   $199.65   $199.60  
  Purchase #3 $16.39   10.650%   $18.1355   $18.14   $18.15   $18.10  
  Purchase #4 $151.52   8.558%   $164.4871   $164.49   $164.50   $164.50  
  Purchase #5 $75.84   10.612%   $83.8881   $83.89   $83.90   $83.90  
  Purchase #6 $83.56   6.288%   $88.8143   $88.81   $88.80   $88.80  
  Purchase #7 $101.96   5.395%   $107.4607   $107.46   $107.45   $107.50  
  7 purchase totals = $651.31       $711.0467   $711.05   $711.10   $711.00