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 $88.86   4.379%   $92.7512   $92.75   $92.75   $92.80  
  Purchase #2 $141.35   13.268%   $160.1043   $160.10   $160.10   $160.10  
  Purchase #3 $187.27   4.632%   $195.9443   $195.94   $195.95   $195.90  
  Purchase #4 $154.71   3.229%   $159.7056   $159.71   $159.70   $159.70  
  Purchase #5 $58.47   12.587%   $65.8296   $65.83   $65.85   $65.80  
  Purchase #6 $214.38   13.450%   $243.2141   $243.21   $243.20   $243.20  
  Purchase #7 $71.62   9.844%   $78.6703   $78.67   $78.65   $78.70  
  7 purchase totals = $916.66       $996.2194   $996.21   $996.20   $996.20