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 $246.83   6.514%   $262.9085   $262.91   $262.90   $262.90  
  Purchase #2 $211.78   8.575%   $229.9401   $229.94   $229.95   $229.90  
  Purchase #3 $214.31   3.870%   $222.6038   $222.60   $222.60   $222.60  
  Purchase #4 $219.49   7.308%   $235.5303   $235.53   $235.55   $235.50  
  Purchase #5 $185.98   7.175%   $199.3241   $199.32   $199.30   $199.30  
  Purchase #6 $149.34   13.163%   $168.9976   $169.00   $169.00   $169.00  
  Purchase #7 $165.66   9.830%   $181.9444   $181.94   $181.95   $181.90  
  7 purchase totals = $1,393.39       $1,501.2488   $1,501.24   $1,501.25   $1,501.10