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 $60.82   9.792%   $66.7755   $66.78   $66.80   $66.80  
  Purchase #2 $38.95   11.843%   $43.5628   $43.56   $43.55   $43.60  
  Purchase #3 $31.36   10.565%   $34.6732   $34.67   $34.65   $34.70  
  Purchase #4 $38.58   9.417%   $42.2131   $42.21   $42.20   $42.20  
  Purchase #5 $209.28   8.415%   $226.8909   $226.89   $226.90   $226.90  
  Purchase #6 $182.81   9.325%   $199.857   $199.86   $199.85   $199.90  
  Purchase #7 $129.91   9.305%   $141.9981   $142.00   $142.00   $142.00  
  7 purchase totals = $691.71       $755.9706   $755.97   $755.95   $756.10