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 $76.90   6.814%   $82.14   $82.14   $82.15   $82.10  
  Purchase #2 $148.32   12.265%   $166.5114   $166.51   $166.50   $166.50  
  Purchase #3 $32.26   7.782%   $34.7705   $34.77   $34.75   $34.80  
  Purchase #4 $241.88   7.798%   $260.7418   $260.74   $260.75   $260.70  
  Purchase #5 $242.81   9.778%   $266.552   $266.55   $266.55   $266.60  
  Purchase #6 $216.38   13.767%   $246.169   $246.17   $246.15   $246.20  
  Purchase #7 $200.37   6.790%   $213.9751   $213.98   $214.00   $214.00  
  7 purchase totals = $1,158.92       $1,270.8598   $1,270.86   $1,270.85   $1,270.90