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 $94.96   3.558%   $98.3387   $98.34   $98.35   $98.30  
  Purchase #2 $192.38   6.486%   $204.8578   $204.86   $204.85   $204.90  
  Purchase #3 $155.70   12.139%   $174.6004   $174.60   $174.60   $174.60  
  Purchase #4 $169.93   4.266%   $177.1792   $177.18   $177.20   $177.20  
  Purchase #5 $100.85   8.702%   $109.626   $109.63   $109.65   $109.60  
  Purchase #6 $35.41   5.843%   $37.479   $37.48   $37.50   $37.50  
  Purchase #7 $48.49   5.426%   $51.1211   $51.12   $51.10   $51.10  
  7 purchase totals = $797.72       $853.2022   $853.21   $853.25   $853.20