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 $49.74   4.628%   $52.042   $52.04   $52.05   $52.00  
  Purchase #2 $235.45   3.469%   $243.6178   $243.62   $243.60   $243.60  
  Purchase #3 $154.78   5.195%   $162.8208   $162.82   $162.80   $162.80  
  Purchase #4 $239.98   7.316%   $257.5369   $257.54   $257.55   $257.50  
  Purchase #5 $146.85   11.192%   $163.2855   $163.29   $163.30   $163.30  
  Purchase #6 $119.72   5.560%   $126.3764   $126.38   $126.40   $126.40  
  Purchase #7 $34.35   6.531%   $36.5934   $36.59   $36.60   $36.60  
  7 purchase totals = $980.87       $1,042.2728   $1,042.28   $1,042.30   $1,042.20