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 $59.89   10.703%   $66.3   $66.30   $66.30   $66.30  
  Purchase #2 $236.53   10.286%   $260.8595   $260.86   $260.85   $260.90  
  Purchase #3 $187.65   9.570%   $205.6081   $205.61   $205.60   $205.60  
  Purchase #4 $214.60   13.163%   $242.8478   $242.85   $242.85   $242.80  
  Purchase #5 $166.28   7.291%   $178.4035   $178.40   $178.40   $178.40  
  Purchase #6 $228.29   6.632%   $243.4302   $243.43   $243.45   $243.40  
  Purchase #7 $214.80   13.644%   $244.1073   $244.11   $244.10   $244.10  
  7 purchase totals = $1,308.04       $1,441.5564   $1,441.56   $1,441.55   $1,441.50