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 $69.29   10.652%   $76.6708   $76.67   $76.65   $76.70  
  Purchase #2 $16.58   5.117%   $17.4284   $17.43   $17.45   $17.40  
  Purchase #3 $19.34   7.289%   $20.7497   $20.75   $20.75   $20.70  
  Purchase #4 $158.91   4.152%   $165.5079   $165.51   $165.50   $165.50  
  Purchase #5 $15.38   10.498%   $16.9946   $16.99   $17.00   $17.00  
  Purchase #6 $190.49   3.661%   $197.4638   $197.46   $197.45   $197.50  
  Purchase #7 $235.38   3.236%   $242.9969   $243.00   $243.00   $243.00  
  7 purchase totals = $705.37       $737.8121   $737.81   $737.80   $737.80