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 $236.63   5.314%   $249.2045   $249.20   $249.20   $249.20  
  Purchase #2 $119.37   4.752%   $125.0425   $125.04   $125.05   $125.00  
  Purchase #3 $161.66   4.124%   $168.3269   $168.33   $168.35   $168.30  
  Purchase #4 $248.29   3.732%   $257.5562   $257.56   $257.55   $257.60  
  Purchase #5 $174.70   5.479%   $184.2718   $184.27   $184.25   $184.30  
  Purchase #6 $127.29   8.798%   $138.489   $138.49   $138.50   $138.50  
  Purchase #7 $167.44   7.160%   $179.4287   $179.43   $179.45   $179.40  
  7 purchase totals = $1,235.38       $1,302.3196   $1,302.32   $1,302.35   $1,302.30