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 $191.75   7.781%   $206.6701   $206.67   $206.65   $206.70  
  Purchase #2 $211.90   9.421%   $231.8631   $231.86   $231.85   $231.90  
  Purchase #3 $111.58   4.519%   $116.6223   $116.62   $116.60   $116.60  
  Purchase #4 $125.71   3.178%   $129.7051   $129.71   $129.70   $129.70  
  Purchase #5 $61.62   7.105%   $65.9981   $66.00   $66.00   $66.00  
  Purchase #6 $237.51   11.208%   $264.1301   $264.13   $264.15   $264.10  
  Purchase #7 $7.92   8.728%   $8.6113   $8.61   $8.60   $8.60  
  7 purchase totals = $947.99       $1,023.6001   $1,023.60   $1,023.55   $1,023.60