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 $9.40   5.588%   $9.9253   $9.93   $9.95   $9.90  
  Purchase #2 $166.92   5.573%   $176.2225   $176.22   $176.20   $176.20  
  Purchase #3 $27.82   7.569%   $29.9257   $29.93   $29.95   $29.90  
  Purchase #4 $75.32   8.761%   $81.9188   $81.92   $81.90   $81.90  
  Purchase #5 $104.96   5.259%   $110.4798   $110.48   $110.50   $110.50  
  Purchase #6 $124.49   3.609%   $128.9828   $128.98   $129.00   $129.00  
  Purchase #7 $48.73   4.732%   $51.0359   $51.04   $51.05   $51.00  
  7 purchase totals = $557.64       $588.4908   $588.50   $588.55   $588.40