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 $247.56   6.872%   $264.5723   $264.57   $264.55   $264.60  
  Purchase #2 $41.29   9.620%   $45.2621   $45.26   $45.25   $45.30  
  Purchase #3 $71.53   5.858%   $75.7202   $75.72   $75.70   $75.70  
  Purchase #4 $61.53   6.679%   $65.6396   $65.64   $65.65   $65.60  
  Purchase #5 $197.55   8.444%   $214.2311   $214.23   $214.25   $214.20  
  Purchase #6 $166.48   12.193%   $186.7789   $186.78   $186.80   $186.80  
  Purchase #7 $125.39   4.398%   $130.9047   $130.90   $130.90   $130.90  
  7 purchase totals = $911.33       $983.1089   $983.10   $983.10   $983.10