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 $57.82   9.431%   $63.273   $63.27   $63.25   $63.30  
  Purchase #2 $219.68   12.711%   $247.6035   $247.60   $247.60   $247.60  
  Purchase #3 $237.34   9.858%   $260.737   $260.74   $260.75   $260.70  
  Purchase #4 $127.85   6.297%   $135.9007   $135.90   $135.90   $135.90  
  Purchase #5 $177.28   10.352%   $195.632   $195.63   $195.65   $195.60  
  Purchase #6 $239.58   3.718%   $248.4876   $248.49   $248.50   $248.50  
  Purchase #7 $229.45   11.567%   $255.9905   $255.99   $256.00   $256.00  
  7 purchase totals = $1,289.00       $1,407.6243   $1,407.62   $1,407.65   $1,407.60