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 $23.26   13.205%   $26.3315   $26.33   $26.35   $26.30  
  Purchase #2 $161.31   3.610%   $167.1333   $167.13   $167.15   $167.10  
  Purchase #3 $157.29   12.202%   $176.4825   $176.48   $176.50   $176.50  
  Purchase #4 $206.37   13.108%   $233.421   $233.42   $233.40   $233.40  
  Purchase #5 $125.78   8.738%   $136.7707   $136.77   $136.75   $136.80  
  Purchase #6 $207.35   9.564%   $227.181   $227.18   $227.20   $227.20  
  Purchase #7 $42.30   4.216%   $44.0834   $44.08   $44.10   $44.10  
  7 purchase totals = $923.66       $1,011.4034   $1,011.39   $1,011.45   $1,011.40