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 $101.72   12.252%   $114.1827   $114.18   $114.20   $114.20  
  Purchase #2 $118.42   3.591%   $122.6725   $122.67   $122.65   $122.70  
  Purchase #3 $27.53   7.112%   $29.4879   $29.49   $29.50   $29.50  
  Purchase #4 $61.75   4.627%   $64.6072   $64.61   $64.60   $64.60  
  Purchase #5 $111.75   13.352%   $126.6709   $126.67   $126.65   $126.70  
  Purchase #6 $33.99   9.585%   $37.2479   $37.25   $37.25   $37.20  
  Purchase #7 $6.78   8.854%   $7.3803   $7.38   $7.40   $7.40  
  7 purchase totals = $461.94       $502.2494   $502.25   $502.25   $502.30