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 $92.55   3.841%   $96.1048   $96.10   $96.10   $96.10  
  Purchase #2 $28.65   12.634%   $32.2696   $32.27   $32.25   $32.30  
  Purchase #3 $97.66   5.202%   $102.7403   $102.74   $102.75   $102.70  
  Purchase #4 $188.93   7.751%   $203.574   $203.57   $203.55   $203.60  
  Purchase #5 $107.58   6.460%   $114.5297   $114.53   $114.55   $114.50  
  Purchase #6 $177.98   9.414%   $194.735   $194.74   $194.75   $194.70  
  Purchase #7 $250.95   11.749%   $280.4341   $280.43   $280.45   $280.40  
  7 purchase totals = $944.30       $1,024.3875   $1,024.38   $1,024.40   $1,024.30