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 $11.44   8.718%   $12.4373   $12.44   $12.45   $12.40  
  Purchase #2 $195.83   5.367%   $206.3402   $206.34   $206.35   $206.30  
  Purchase #3 $130.76   5.159%   $137.5059   $137.51   $137.50   $137.50  
  Purchase #4 $92.33   4.206%   $96.2134   $96.21   $96.20   $96.20  
  Purchase #5 $193.85   8.793%   $210.8952   $210.90   $210.90   $210.90  
  Purchase #6 $169.82   12.290%   $190.6909   $190.69   $190.70   $190.70  
  Purchase #7 $56.74   6.284%   $60.3055   $60.31   $60.30   $60.30  
  7 purchase totals = $850.77       $914.3884   $914.40   $914.40   $914.30