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 $60.40   13.588%   $68.6072   $68.61   $68.60   $68.60  
  Purchase #2 $214.57   12.625%   $241.6595   $241.66   $241.65   $241.70  
  Purchase #3 $66.33   13.651%   $75.3847   $75.38   $75.40   $75.40  
  Purchase #4 $112.27   7.516%   $120.7082   $120.71   $120.70   $120.70  
  Purchase #5 $154.78   4.352%   $161.516   $161.52   $161.50   $161.50  
  Purchase #6 $76.97   7.472%   $82.7212   $82.72   $82.70   $82.70  
  Purchase #7 $87.71   6.831%   $93.7015   $93.70   $93.70   $93.70  
  7 purchase totals = $773.03       $844.2983   $844.30   $844.25   $844.30