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 $246.76   6.288%   $262.2763   $262.28   $262.30   $262.30  
  Purchase #2 $217.34   3.318%   $224.5513   $224.55   $224.55   $224.60  
  Purchase #3 $41.63   13.455%   $47.2313   $47.23   $47.25   $47.20  
  Purchase #4 $21.79   12.538%   $24.522   $24.52   $24.50   $24.50  
  Purchase #5 $164.50   8.346%   $178.2292   $178.23   $178.25   $178.20  
  Purchase #6 $120.29   12.590%   $135.4345   $135.43   $135.45   $135.40  
  Purchase #7 $156.49   10.729%   $173.2798   $173.28   $173.30   $173.30  
  7 purchase totals = $968.80       $1,045.5244   $1,045.52   $1,045.60   $1,045.50