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 $68.86   11.807%   $76.9903   $76.99   $77.00   $77.00  
  Purchase #2 $25.97   4.121%   $27.0402   $27.04   $27.05   $27.00  
  Purchase #3 $141.63   13.582%   $160.8662   $160.87   $160.85   $160.90  
  Purchase #4 $250.42   8.220%   $271.0045   $271.00   $271.00   $271.00  
  Purchase #5 $213.90   13.204%   $242.1434   $242.14   $242.15   $242.10  
  Purchase #6 $244.43   10.388%   $269.8214   $269.82   $269.80   $269.80  
  Purchase #7 $221.79   13.266%   $251.2127   $251.21   $251.20   $251.20  
  7 purchase totals = $1,167.00       $1,299.0787   $1,299.07   $1,299.05   $1,299.00