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 $239.58   13.680%   $272.3545   $272.35   $272.35   $272.40  
  Purchase #2 $194.29   5.172%   $204.3387   $204.34   $204.35   $204.30  
  Purchase #3 $247.79   11.389%   $276.0108   $276.01   $276.00   $276.00  
  Purchase #4 $57.97   4.520%   $60.5902   $60.59   $60.60   $60.60  
  Purchase #5 $98.67   8.800%   $107.353   $107.35   $107.35   $107.40  
  Purchase #6 $54.29   12.498%   $61.0752   $61.08   $61.10   $61.10  
  Purchase #7 $81.34   8.110%   $87.9367   $87.94   $87.95   $87.90  
  7 purchase totals = $973.93       $1,069.6591   $1,069.66   $1,069.70   $1,069.70