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 $87.56   8.311%   $94.8371   $94.84   $94.85   $94.80  
  Purchase #2 $115.99   13.869%   $132.0767   $132.08   $132.10   $132.10  
  Purchase #3 $124.95   13.313%   $141.5846   $141.58   $141.60   $141.60  
  Purchase #4 $203.78   9.232%   $222.593   $222.59   $222.60   $222.60  
  Purchase #5 $138.85   11.166%   $154.354   $154.35   $154.35   $154.40  
  Purchase #6 $65.68   4.648%   $68.7328   $68.73   $68.75   $68.70  
  Purchase #7 $34.38   7.400%   $36.9241   $36.92   $36.90   $36.90  
  7 purchase totals = $771.19       $851.1023   $851.09   $851.15   $851.10