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 $48.70   10.559%   $53.8422   $53.84   $53.85   $53.80  
  Purchase #2 $187.85   9.567%   $205.8216   $205.82   $205.80   $205.80  
  Purchase #3 $96.94   11.819%   $108.3973   $108.40   $108.40   $108.40  
  Purchase #4 $73.49   4.194%   $76.5722   $76.57   $76.55   $76.60  
  Purchase #5 $11.62   5.555%   $12.2655   $12.27   $12.25   $12.30  
  Purchase #6 $229.81   3.731%   $238.3842   $238.38   $238.40   $238.40  
  Purchase #7 $43.44   13.737%   $49.4074   $49.41   $49.40   $49.40  
  7 purchase totals = $691.85       $744.6904   $744.69   $744.65   $744.70