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 $67.66   8.764%   $73.5897   $73.59   $73.60   $73.60  
  Purchase #2 $153.34   13.551%   $174.1191   $174.12   $174.10   $174.10  
  Purchase #3 $48.51   11.383%   $54.0319   $54.03   $54.05   $54.00  
  Purchase #4 $134.33   4.225%   $140.0054   $140.01   $140.00   $140.00  
  Purchase #5 $247.38   5.814%   $261.7627   $261.76   $261.75   $261.80  
  Purchase #6 $169.38   10.580%   $187.3004   $187.30   $187.30   $187.30  
  Purchase #7 $156.26   13.525%   $177.3942   $177.39   $177.40   $177.40  
  7 purchase totals = $976.86       $1,068.2034   $1,068.20   $1,068.20   $1,068.20