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 $70.61   8.732%   $76.7757   $76.78   $76.80   $76.80  
  Purchase #2 $247.38   8.517%   $268.4494   $268.45   $268.45   $268.40  
  Purchase #3 $175.42   11.849%   $196.2055   $196.21   $196.20   $196.20  
  Purchase #4 $75.42   6.295%   $80.1677   $80.17   $80.15   $80.20  
  Purchase #5 $227.99   7.596%   $245.3081   $245.31   $245.30   $245.30  
  Purchase #6 $47.63   6.266%   $50.6145   $50.61   $50.60   $50.60  
  Purchase #7 $24.36   4.225%   $25.3892   $25.39   $25.40   $25.40  
  7 purchase totals = $868.81       $942.9101   $942.92   $942.90   $942.90