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 $61.45   8.437%   $66.6345   $66.63   $66.65   $66.60  
  Purchase #2 $224.91   6.866%   $240.3523   $240.35   $240.35   $240.40  
  Purchase #3 $75.36   9.184%   $82.2811   $82.28   $82.30   $82.30  
  Purchase #4 $249.68   3.784%   $259.1279   $259.13   $259.15   $259.10  
  Purchase #5 $13.26   5.639%   $14.0077   $14.01   $14.00   $14.00  
  Purchase #6 $155.53   7.325%   $166.9226   $166.92   $166.90   $166.90  
  Purchase #7 $26.59   7.275%   $28.5244   $28.52   $28.50   $28.50  
  7 purchase totals = $806.78       $857.8505   $857.84   $857.85   $857.80