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 $224.80   9.117%   $245.295   $245.30   $245.30   $245.30  
  Purchase #2 $62.76   4.642%   $65.6733   $65.67   $65.65   $65.70  
  Purchase #3 $109.47   7.769%   $117.9747   $117.97   $117.95   $118.00  
  Purchase #4 $103.44   9.655%   $113.4271   $113.43   $113.45   $113.40  
  Purchase #5 $176.37   13.187%   $199.6279   $199.63   $199.65   $199.60  
  Purchase #6 $250.74   6.686%   $267.5045   $267.50   $267.50   $267.50  
  Purchase #7 $97.72   13.272%   $110.6894   $110.69   $110.70   $110.70  
  7 purchase totals = $1,025.30       $1,120.1919   $1,120.19   $1,120.20   $1,120.20