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 $167.42   9.290%   $182.9733   $182.97   $182.95   $183.00  
  Purchase #2 $226.53   13.282%   $256.6177   $256.62   $256.60   $256.60  
  Purchase #3 $75.47   6.459%   $80.3446   $80.34   $80.35   $80.30  
  Purchase #4 $240.75   9.725%   $264.1629   $264.16   $264.15   $264.20  
  Purchase #5 $158.44   6.487%   $168.718   $168.72   $168.70   $168.70  
  Purchase #6 $26.90   9.747%   $29.5219   $29.52   $29.50   $29.50  
  Purchase #7 $176.58   13.237%   $199.9539   $199.95   $199.95   $200.00  
  7 purchase totals = $1,072.09       $1,182.2923   $1,182.28   $1,182.20   $1,182.30