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 $62.66   9.155%   $68.3965   $68.40   $68.40   $68.40  
  Purchase #2 $244.26   7.399%   $262.3328   $262.33   $262.35   $262.30  
  Purchase #3 $9.32   7.735%   $10.0409   $10.04   $10.05   $10.00  
  Purchase #4 $227.80   5.742%   $240.8803   $240.88   $240.90   $240.90  
  Purchase #5 $132.66   10.763%   $146.9382   $146.94   $146.95   $146.90  
  Purchase #6 $126.72   9.153%   $138.3187   $138.32   $138.30   $138.30  
  Purchase #7 $163.83   5.445%   $172.7505   $172.75   $172.75   $172.80  
  7 purchase totals = $967.25       $1,039.6579   $1,039.66   $1,039.70   $1,039.60