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 $211.52   7.206%   $226.7621   $226.76   $226.75   $226.80  
  Purchase #2 $183.59   9.661%   $201.3266   $201.33   $201.35   $201.30  
  Purchase #3 $74.38   10.779%   $82.3974   $82.40   $82.40   $82.40  
  Purchase #4 $51.62   13.567%   $58.6233   $58.62   $58.60   $58.60  
  Purchase #5 $58.49   5.616%   $61.7748   $61.77   $61.75   $61.80  
  Purchase #6 $98.58   10.582%   $109.0117   $109.01   $109.00   $109.00  
  Purchase #7 $197.95   5.590%   $209.0154   $209.02   $209.00   $209.00  
  7 purchase totals = $876.13       $948.9113   $948.91   $948.85   $948.90