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 $88.52   13.562%   $100.5251   $100.53   $100.55   $100.50  
  Purchase #2 $116.57   12.239%   $130.837   $130.84   $130.85   $130.80  
  Purchase #3 $48.28   10.497%   $53.348   $53.35   $53.35   $53.30  
  Purchase #4 $195.28   8.804%   $212.4725   $212.47   $212.45   $212.50  
  Purchase #5 $13.35   4.392%   $13.9363   $13.94   $13.95   $13.90  
  Purchase #6 $245.89   10.828%   $272.515   $272.52   $272.50   $272.50  
  Purchase #7 $156.96   6.528%   $167.2063   $167.21   $167.20   $167.20  
  7 purchase totals = $864.85       $950.8402   $950.86   $950.85   $950.70