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 $56.58   7.386%   $60.759   $60.76   $60.75   $60.80  
  Purchase #2 $61.40   8.692%   $66.7369   $66.74   $66.75   $66.70  
  Purchase #3 $102.39   3.580%   $106.0556   $106.06   $106.05   $106.10  
  Purchase #4 $76.90   5.703%   $81.2856   $81.29   $81.30   $81.30  
  Purchase #5 $89.42   7.355%   $95.9968   $96.00   $96.00   $96.00  
  Purchase #6 $201.76   5.608%   $213.0747   $213.07   $213.05   $213.10  
  Purchase #7 $169.45   12.279%   $190.2568   $190.26   $190.25   $190.30  
  7 purchase totals = $757.90       $814.1654   $814.18   $814.15   $814.30