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 $204.35   5.487%   $215.5627   $215.56   $215.55   $215.60  
  Purchase #2 $61.97   9.356%   $67.7679   $67.77   $67.75   $67.80  
  Purchase #3 $237.34   5.776%   $251.0488   $251.05   $251.05   $251.00  
  Purchase #4 $84.38   11.315%   $93.9276   $93.93   $93.95   $93.90  
  Purchase #5 $246.44   7.705%   $265.4282   $265.43   $265.45   $265.40  
  Purchase #6 $235.62   8.519%   $255.6925   $255.69   $255.70   $255.70  
  Purchase #7 $42.29   13.513%   $48.0046   $48.00   $48.00   $48.00  
  7 purchase totals = $1,112.39       $1,197.4323   $1,197.43   $1,197.45   $1,197.40