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 $12.93   8.716%   $14.057   $14.06   $14.05   $14.10  
  Purchase #2 $27.97   9.249%   $30.5569   $30.56   $30.55   $30.60  
  Purchase #3 $11.91   5.640%   $12.5817   $12.58   $12.60   $12.60  
  Purchase #4 $92.60   7.858%   $99.8765   $99.88   $99.90   $99.90  
  Purchase #5 $232.73   5.390%   $245.2741   $245.27   $245.25   $245.30  
  Purchase #6 $87.98   7.480%   $94.5609   $94.56   $94.55   $94.60  
  Purchase #7 $94.93   13.629%   $107.868   $107.87   $107.85   $107.90  
  7 purchase totals = $561.05       $604.7751   $604.78   $604.75   $605.00