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 $202.36   6.267%   $215.0419   $215.04   $215.05   $215.00  
  Purchase #2 $115.57   9.767%   $126.8577   $126.86   $126.85   $126.90  
  Purchase #3 $93.89   7.532%   $100.9618   $100.96   $100.95   $101.00  
  Purchase #4 $20.85   6.345%   $22.1729   $22.17   $22.15   $22.20  
  Purchase #5 $211.53   13.334%   $239.7354   $239.74   $239.75   $239.70  
  Purchase #6 $67.88   9.408%   $74.2662   $74.27   $74.25   $74.30  
  Purchase #7 $22.76   11.635%   $25.4081   $25.41   $25.40   $25.40  
  7 purchase totals = $734.84       $804.4440   $804.45   $804.40   $804.50