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 $9.55   12.178%   $10.713   $10.71   $10.70   $10.70  
  Purchase #2 $138.76   7.492%   $149.1559   $149.16   $149.15   $149.20  
  Purchase #3 $38.93   9.508%   $42.6315   $42.63   $42.65   $42.60  
  Purchase #4 $13.59   3.805%   $14.1071   $14.11   $14.10   $14.10  
  Purchase #5 $108.33   4.186%   $112.8647   $112.86   $112.85   $112.90  
  Purchase #6 $12.62   9.140%   $13.7735   $13.77   $13.75   $13.80  
  Purchase #7 $216.55   4.520%   $226.3381   $226.34   $226.35   $226.30  
  7 purchase totals = $538.33       $569.5838   $569.58   $569.55   $569.60