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 $12.48   11.763%   $13.948   $13.95   $13.95   $13.90  
  Purchase #2 $175.49   4.579%   $183.5257   $183.53   $183.55   $183.50  
  Purchase #3 $150.80   9.383%   $164.9496   $164.95   $164.95   $164.90  
  Purchase #4 $245.34   6.217%   $260.5928   $260.59   $260.60   $260.60  
  Purchase #5 $109.64   13.865%   $124.8416   $124.84   $124.85   $124.80  
  Purchase #6 $39.59   12.104%   $44.382   $44.38   $44.40   $44.40  
  Purchase #7 $131.64   5.429%   $138.7867   $138.79   $138.80   $138.80  
  7 purchase totals = $864.98       $931.0264   $931.03   $931.10   $930.90