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 $222.43   11.423%   $247.8382   $247.84   $247.85   $247.80  
  Purchase #2 $196.81   13.757%   $223.8852   $223.89   $223.90   $223.90  
  Purchase #3 $14.52   4.373%   $15.155   $15.16   $15.15   $15.20  
  Purchase #4 $95.82   5.757%   $101.3364   $101.34   $101.35   $101.30  
  Purchase #5 $62.97   7.179%   $67.4906   $67.49   $67.50   $67.50  
  Purchase #6 $106.96   4.618%   $111.8994   $111.90   $111.90   $111.90  
  Purchase #7 $31.99   4.442%   $33.411   $33.41   $33.40   $33.40  
  7 purchase totals = $731.50       $801.0158   $801.03   $801.05   $801.00