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 $204.85   8.599%   $222.4651   $222.47   $222.45   $222.50  
  Purchase #2 $150.34   8.763%   $163.5143   $163.51   $163.50   $163.50  
  Purchase #3 $22.84   8.664%   $24.8189   $24.82   $24.80   $24.80  
  Purchase #4 $62.26   5.759%   $65.8456   $65.85   $65.85   $65.80  
  Purchase #5 $78.94   5.103%   $82.9683   $82.97   $82.95   $83.00  
  Purchase #6 $221.73   11.598%   $247.4462   $247.45   $247.45   $247.40  
  Purchase #7 $180.62   7.738%   $194.5964   $194.60   $194.60   $194.60  
  7 purchase totals = $921.58       $1,001.6548   $1,001.67   $1,001.60   $1,001.60