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 $60.46   8.625%   $65.6747   $65.67   $65.65   $65.70  
  Purchase #2 $30.36   12.651%   $34.2008   $34.20   $34.20   $34.20  
  Purchase #3 $67.90   7.284%   $72.8458   $72.85   $72.85   $72.80  
  Purchase #4 $40.97   11.834%   $45.8184   $45.82   $45.80   $45.80  
  Purchase #5 $231.56   11.858%   $259.0184   $259.02   $259.00   $259.00  
  Purchase #6 $53.51   3.119%   $55.179   $55.18   $55.20   $55.20  
  Purchase #7 $236.53   9.207%   $258.3073   $258.31   $258.30   $258.30  
  7 purchase totals = $721.29       $791.0444   $791.05   $791.00   $791.00