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 $199.55   13.276%   $226.0423   $226.04   $226.05   $226.00  
  Purchase #2 $51.79   7.508%   $55.6784   $55.68   $55.70   $55.70  
  Purchase #3 $68.28   12.158%   $76.5815   $76.58   $76.60   $76.60  
  Purchase #4 $108.52   9.804%   $119.1593   $119.16   $119.15   $119.20  
  Purchase #5 $63.45   6.590%   $67.6314   $67.63   $67.65   $67.60  
  Purchase #6 $63.46   3.169%   $65.471   $65.47   $65.45   $65.50  
  Purchase #7 $5.52   8.355%   $5.9812   $5.98   $6.00   $6.00  
  7 purchase totals = $560.57       $616.5451   $616.54   $616.60   $616.60