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 $220.44   6.579%   $234.9427   $234.94   $234.95   $234.90  
  Purchase #2 $152.32   8.305%   $164.9702   $164.97   $164.95   $165.00  
  Purchase #3 $17.84   11.517%   $19.8946   $19.89   $19.90   $19.90  
  Purchase #4 $55.87   7.816%   $60.2368   $60.24   $60.25   $60.20  
  Purchase #5 $81.98   7.639%   $88.2425   $88.24   $88.25   $88.20  
  Purchase #6 $71.50   7.659%   $76.9762   $76.98   $77.00   $77.00  
  Purchase #7 $130.89   6.706%   $139.6675   $139.67   $139.65   $139.70  
  7 purchase totals = $730.84       $784.9305   $784.93   $784.95   $784.90