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 $244.94   9.272%   $267.6508   $267.65   $267.65   $267.70  
  Purchase #2 $168.84   6.301%   $179.4786   $179.48   $179.50   $179.50  
  Purchase #3 $175.89   7.226%   $188.5998   $188.60   $188.60   $188.60  
  Purchase #4 $117.64   10.728%   $130.2604   $130.26   $130.25   $130.30  
  Purchase #5 $121.87   11.614%   $136.024   $136.02   $136.00   $136.00  
  Purchase #6 $84.81   4.858%   $88.9301   $88.93   $88.95   $88.90  
  Purchase #7 $245.74   4.307%   $256.324   $256.32   $256.30   $256.30  
  7 purchase totals = $1,159.73       $1,247.2677   $1,247.26   $1,247.25   $1,247.30