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 $195.53   4.444%   $204.2194   $204.22   $204.20   $204.20  
  Purchase #2 $53.87   12.233%   $60.4599   $60.46   $60.45   $60.50  
  Purchase #3 $23.63   13.820%   $26.8957   $26.90   $26.90   $26.90  
  Purchase #4 $57.26   9.686%   $62.8062   $62.81   $62.80   $62.80  
  Purchase #5 $143.94   3.667%   $149.2183   $149.22   $149.20   $149.20  
  Purchase #6 $154.74   6.366%   $164.5907   $164.59   $164.60   $164.60  
  Purchase #7 $245.74   11.723%   $274.5481   $274.55   $274.55   $274.50  
  7 purchase totals = $874.71       $942.7383   $942.75   $942.70   $942.70