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 $169.54   8.707%   $184.3018   $184.30   $184.30   $184.30  
  Purchase #2 $54.88   7.169%   $58.8143   $58.81   $58.80   $58.80  
  Purchase #3 $22.70   11.810%   $25.3809   $25.38   $25.40   $25.40  
  Purchase #4 $247.97   9.648%   $271.8941   $271.89   $271.90   $271.90  
  Purchase #5 $48.95   8.647%   $53.1827   $53.18   $53.20   $53.20  
  Purchase #6 $5.64   9.186%   $6.1581   $6.16   $6.15   $6.20  
  Purchase #7 $113.97   7.829%   $122.8927   $122.89   $122.90   $122.90  
  7 purchase totals = $663.65       $722.6246   $722.61   $722.65   $722.70