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 $85.75   8.662%   $93.1777   $93.18   $93.20   $93.20  
  Purchase #2 $177.57   9.244%   $193.9846   $193.98   $194.00   $194.00  
  Purchase #3 $241.59   11.779%   $270.0469   $270.05   $270.05   $270.00  
  Purchase #4 $247.46   5.620%   $261.3673   $261.37   $261.35   $261.40  
  Purchase #5 $248.45   11.608%   $277.2901   $277.29   $277.30   $277.30  
  Purchase #6 $21.29   6.607%   $22.6966   $22.70   $22.70   $22.70  
  Purchase #7 $62.60   3.406%   $64.7322   $64.73   $64.75   $64.70  
  7 purchase totals = $1,084.71       $1,183.2954   $1,183.30   $1,183.35   $1,183.30