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 $187.89   9.122%   $205.0293   $205.03   $205.05   $205.00  
  Purchase #2 $217.97   4.464%   $227.7002   $227.70   $227.70   $227.70  
  Purchase #3 $108.46   13.312%   $122.8982   $122.90   $122.90   $122.90  
  Purchase #4 $204.94   8.468%   $222.2943   $222.29   $222.30   $222.30  
  Purchase #5 $247.57   9.710%   $271.609   $271.61   $271.60   $271.60  
  Purchase #6 $108.80   12.275%   $122.1552   $122.16   $122.15   $122.20  
  Purchase #7 $244.76   4.364%   $255.4413   $255.44   $255.45   $255.40  
  7 purchase totals = $1,320.39       $1,427.1275   $1,427.13   $1,427.15   $1,427.10