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 $116.96   8.160%   $126.5039   $126.50   $126.50   $126.50  
  Purchase #2 $187.37   4.454%   $195.7155   $195.72   $195.70   $195.70  
  Purchase #3 $132.73   7.128%   $142.191   $142.19   $142.20   $142.20  
  Purchase #4 $85.50   10.692%   $94.6417   $94.64   $94.65   $94.60  
  Purchase #5 $5.68   9.252%   $6.2055   $6.21   $6.20   $6.20  
  Purchase #6 $104.97   4.164%   $109.341   $109.34   $109.35   $109.30  
  Purchase #7 $243.81   4.231%   $254.1256   $254.13   $254.15   $254.10  
  7 purchase totals = $877.02       $928.7242   $928.73   $928.75   $928.60