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 $67.82   12.275%   $76.1449   $76.14   $76.15   $76.10  
  Purchase #2 $42.62   7.544%   $45.8353   $45.84   $45.85   $45.80  
  Purchase #3 $116.95   10.306%   $129.0029   $129.00   $129.00   $129.00  
  Purchase #4 $240.69   11.185%   $267.6112   $267.61   $267.60   $267.60  
  Purchase #5 $153.91   8.321%   $166.7169   $166.72   $166.70   $166.70  
  Purchase #6 $244.99   9.824%   $269.0578   $269.06   $269.05   $269.10  
  Purchase #7 $96.26   7.246%   $103.235   $103.24   $103.25   $103.20  
  7 purchase totals = $963.24       $1,057.6040   $1,057.61   $1,057.60   $1,057.50