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 $23.91   12.624%   $26.9284   $26.93   $26.95   $26.90  
  Purchase #2 $195.83   7.600%   $210.7131   $210.71   $210.70   $210.70  
  Purchase #3 $141.28   11.406%   $157.3944   $157.39   $157.40   $157.40  
  Purchase #4 $196.43   5.259%   $206.7603   $206.76   $206.75   $206.80  
  Purchase #5 $134.86   11.497%   $150.3649   $150.36   $150.35   $150.40  
  Purchase #6 $98.99   7.574%   $106.4875   $106.49   $106.50   $106.50  
  Purchase #7 $184.28   5.245%   $193.9455   $193.95   $193.95   $193.90  
  7 purchase totals = $975.58       $1,052.5941   $1,052.59   $1,052.60   $1,052.60