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 $248.33   13.786%   $282.5648   $282.56   $282.55   $282.60  
  Purchase #2 $187.27   9.792%   $205.6075   $205.61   $205.60   $205.60  
  Purchase #3 $116.43   6.726%   $124.2611   $124.26   $124.25   $124.30  
  Purchase #4 $222.29   5.486%   $234.4848   $234.48   $234.50   $234.50  
  Purchase #5 $153.74   7.176%   $164.7724   $164.77   $164.75   $164.80  
  Purchase #6 $122.64   7.405%   $131.7215   $131.72   $131.70   $131.70  
  Purchase #7 $217.52   7.576%   $233.9993   $234.00   $234.00   $234.00  
  7 purchase totals = $1,268.22       $1,377.4114   $1,377.40   $1,377.35   $1,377.50