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 $239.84   10.574%   $265.2007   $265.20   $265.20   $265.20  
  Purchase #2 $73.26   3.532%   $75.8475   $75.85   $75.85   $75.80  
  Purchase #3 $77.77   5.130%   $81.7596   $81.76   $81.75   $81.80  
  Purchase #4 $193.47   12.808%   $218.2496   $218.25   $218.25   $218.20  
  Purchase #5 $47.78   12.366%   $53.6885   $53.69   $53.70   $53.70  
  Purchase #6 $240.75   11.147%   $267.5864   $267.59   $267.60   $267.60  
  Purchase #7 $77.54   7.416%   $83.2904   $83.29   $83.30   $83.30  
  7 purchase totals = $950.41       $1,045.6227   $1,045.63   $1,045.65   $1,045.60