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 $133.98   8.673%   $145.6001   $145.60   $145.60   $145.60  
  Purchase #2 $178.81   12.277%   $200.7625   $200.76   $200.75   $200.80  
  Purchase #3 $184.47   11.669%   $205.9958   $206.00   $206.00   $206.00  
  Purchase #4 $13.80   3.414%   $14.2711   $14.27   $14.25   $14.30  
  Purchase #5 $137.86   3.277%   $142.3777   $142.38   $142.40   $142.40  
  Purchase #6 $63.71   4.797%   $66.7662   $66.77   $66.75   $66.80  
  Purchase #7 $51.83   12.236%   $58.1719   $58.17   $58.15   $58.20  
  7 purchase totals = $764.46       $833.9453   $833.95   $833.90   $834.10