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 $217.56   12.489%   $244.7311   $244.73   $244.75   $244.70  
  Purchase #2 $118.50   10.552%   $131.0041   $131.00   $131.00   $131.00  
  Purchase #3 $216.75   9.492%   $237.3239   $237.32   $237.30   $237.30  
  Purchase #4 $85.57   10.508%   $94.5617   $94.56   $94.55   $94.60  
  Purchase #5 $232.65   4.388%   $242.8587   $242.86   $242.85   $242.90  
  Purchase #6 $51.82   8.830%   $56.3957   $56.40   $56.40   $56.40  
  Purchase #7 $246.28   11.124%   $273.6762   $273.68   $273.70   $273.70  
  7 purchase totals = $1,169.13       $1,280.5514   $1,280.55   $1,280.55   $1,280.60