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 $84.96   9.362%   $92.914   $92.91   $92.90   $92.90  
  Purchase #2 $114.51   3.497%   $118.5144   $118.51   $118.50   $118.50  
  Purchase #3 $8.77   5.814%   $9.2799   $9.28   $9.30   $9.30  
  Purchase #4 $62.46   11.714%   $69.7766   $69.78   $69.80   $69.80  
  Purchase #5 $219.97   5.428%   $231.91   $231.91   $231.90   $231.90  
  Purchase #6 $228.33   13.404%   $258.9354   $258.94   $258.95   $258.90  
  Purchase #7 $169.51   3.850%   $176.0361   $176.04   $176.05   $176.00  
  7 purchase totals = $888.51       $957.3664   $957.37   $957.40   $957.30