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 $59.39   8.719%   $64.5682   $64.57   $64.55   $64.60  
  Purchase #2 $44.94   7.145%   $48.151   $48.15   $48.15   $48.20  
  Purchase #3 $23.80   5.321%   $25.0664   $25.07   $25.05   $25.10  
  Purchase #4 $46.79   8.553%   $50.7919   $50.79   $50.80   $50.80  
  Purchase #5 $61.78   11.340%   $68.7859   $68.79   $68.80   $68.80  
  Purchase #6 $76.34   9.181%   $83.3488   $83.35   $83.35   $83.30  
  Purchase #7 $207.85   7.650%   $223.7505   $223.75   $223.75   $223.80  
  7 purchase totals = $520.89       $564.4627   $564.47   $564.45   $564.60