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 $115.33   4.632%   $120.6721   $120.67   $120.65   $120.70  
  Purchase #2 $139.58   8.391%   $151.2922   $151.29   $151.30   $151.30  
  Purchase #3 $37.64   6.842%   $40.2153   $40.22   $40.20   $40.20  
  Purchase #4 $62.68   3.628%   $64.954   $64.95   $64.95   $65.00  
  Purchase #5 $243.28   11.779%   $271.936   $271.94   $271.95   $271.90  
  Purchase #6 $184.59   13.455%   $209.4266   $209.43   $209.45   $209.40  
  Purchase #7 $250.68   12.131%   $281.09   $281.09   $281.10   $281.10  
  7 purchase totals = $1,033.78       $1,139.5862   $1,139.59   $1,139.60   $1,139.60