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 $64.81   5.851%   $68.602   $68.60   $68.60   $68.60  
  Purchase #2 $54.34   6.742%   $58.0036   $58.00   $58.00   $58.00  
  Purchase #3 $196.39   3.865%   $203.9805   $203.98   $204.00   $204.00  
  Purchase #4 $142.42   8.285%   $154.2195   $154.22   $154.20   $154.20  
  Purchase #5 $111.85   4.192%   $116.5388   $116.54   $116.55   $116.50  
  Purchase #6 $158.28   3.200%   $163.345   $163.35   $163.35   $163.30  
  Purchase #7 $156.51   13.172%   $177.1255   $177.13   $177.15   $177.10  
  7 purchase totals = $884.60       $941.8149   $941.82   $941.85   $941.70