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 $186.48   5.715%   $197.1373   $197.14   $197.15   $197.10  
  Purchase #2 $146.40   11.111%   $162.6665   $162.67   $162.65   $162.70  
  Purchase #3 $233.66   10.367%   $257.8835   $257.88   $257.90   $257.90  
  Purchase #4 $248.29   7.263%   $266.3233   $266.32   $266.30   $266.30  
  Purchase #5 $97.86   11.804%   $109.4114   $109.41   $109.40   $109.40  
  Purchase #6 $5.76   11.313%   $6.4116   $6.41   $6.40   $6.40  
  Purchase #7 $75.79   12.188%   $85.0273   $85.03   $85.05   $85.00  
  7 purchase totals = $994.24       $1,084.8609   $1,084.86   $1,084.85   $1,084.80