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 $56.35   9.455%   $61.6779   $61.68   $61.70   $61.70  
  Purchase #2 $191.52   4.228%   $199.6175   $199.62   $199.60   $199.60  
  Purchase #3 $164.30   6.245%   $174.5605   $174.56   $174.55   $174.60  
  Purchase #4 $169.45   5.204%   $178.2682   $178.27   $178.25   $178.30  
  Purchase #5 $242.34   6.728%   $258.6446   $258.64   $258.65   $258.60  
  Purchase #6 $35.69   10.414%   $39.4068   $39.41   $39.40   $39.40  
  Purchase #7 $18.61   11.819%   $20.8095   $20.81   $20.80   $20.80  
  7 purchase totals = $878.26       $932.9850   $932.99   $932.95   $933.00