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 $176.66   10.854%   $195.8347   $195.83   $195.85   $195.80  
  Purchase #2 $58.28   12.114%   $65.34   $65.34   $65.35   $65.30  
  Purchase #3 $23.85   7.865%   $25.7258   $25.73   $25.75   $25.70  
  Purchase #4 $92.90   11.347%   $103.4414   $103.44   $103.45   $103.40  
  Purchase #5 $13.33   12.229%   $14.9601   $14.96   $14.95   $15.00  
  Purchase #6 $250.65   4.260%   $261.3277   $261.33   $261.35   $261.30  
  Purchase #7 $229.52   8.603%   $249.2656   $249.27   $249.25   $249.30  
  7 purchase totals = $845.19       $915.8953   $915.90   $915.95   $915.80