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 $248.51   11.287%   $276.5593   $276.56   $276.55   $276.60  
  Purchase #2 $231.31   9.657%   $253.6476   $253.65   $253.65   $253.60  
  Purchase #3 $64.89   3.699%   $67.2903   $67.29   $67.30   $67.30  
  Purchase #4 $48.99   13.353%   $55.5316   $55.53   $55.55   $55.50  
  Purchase #5 $235.95   6.534%   $251.367   $251.37   $251.35   $251.40  
  Purchase #6 $173.81   12.321%   $195.2251   $195.23   $195.25   $195.20  
  Purchase #7 $176.93   10.179%   $194.9397   $194.94   $194.95   $194.90  
  7 purchase totals = $1,180.39       $1,294.5606   $1,294.57   $1,294.60   $1,294.50