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 $42.72   9.212%   $46.6554   $46.66   $46.65   $46.70  
  Purchase #2 $29.41   11.371%   $32.7542   $32.75   $32.75   $32.80  
  Purchase #3 $200.50   3.466%   $207.4493   $207.45   $207.45   $207.40  
  Purchase #4 $195.42   3.457%   $202.1757   $202.18   $202.20   $202.20  
  Purchase #5 $6.66   9.493%   $7.2922   $7.29   $7.30   $7.30  
  Purchase #6 $61.39   5.338%   $64.667   $64.67   $64.65   $64.70  
  Purchase #7 $161.72   9.147%   $176.5125   $176.51   $176.50   $176.50  
  7 purchase totals = $697.82       $737.5063   $737.51   $737.50   $737.60