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 $23.83   5.733%   $25.1962   $25.20   $25.20   $25.20  
  Purchase #2 $98.91   12.125%   $110.9028   $110.90   $110.90   $110.90  
  Purchase #3 $91.44   5.385%   $96.364   $96.36   $96.35   $96.40  
  Purchase #4 $186.80   12.295%   $209.7671   $209.77   $209.75   $209.80  
  Purchase #5 $150.25   5.381%   $158.335   $158.34   $158.35   $158.30  
  Purchase #6 $237.61   4.235%   $247.6728   $247.67   $247.65   $247.70  
  Purchase #7 $42.31   13.560%   $48.0472   $48.05   $48.05   $48.00  
  7 purchase totals = $831.15       $896.2851   $896.29   $896.25   $896.30