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 $44.53   11.563%   $49.679   $49.68   $49.70   $49.70  
  Purchase #2 $113.29   13.484%   $128.566   $128.57   $128.55   $128.60  
  Purchase #3 $239.33   7.478%   $257.2271   $257.23   $257.25   $257.20  
  Purchase #4 $178.55   5.147%   $187.74   $187.74   $187.75   $187.70  
  Purchase #5 $72.90   7.482%   $78.3544   $78.35   $78.35   $78.40  
  Purchase #6 $71.70   9.323%   $78.3846   $78.38   $78.40   $78.40  
  Purchase #7 $161.89   13.520%   $183.7775   $183.78   $183.80   $183.80  
  7 purchase totals = $882.19       $963.7286   $963.73   $963.80   $963.80