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 $31.58   11.866%   $35.3273   $35.33   $35.35   $35.30  
  Purchase #2 $188.73   10.332%   $208.2296   $208.23   $208.25   $208.20  
  Purchase #3 $231.34   10.559%   $255.7672   $255.77   $255.75   $255.80  
  Purchase #4 $70.93   3.148%   $73.1629   $73.16   $73.15   $73.20  
  Purchase #5 $219.35   9.528%   $240.2497   $240.25   $240.25   $240.20  
  Purchase #6 $239.50   13.437%   $271.6816   $271.68   $271.70   $271.70  
  Purchase #7 $69.33   5.738%   $73.3082   $73.31   $73.30   $73.30  
  7 purchase totals = $1,050.76       $1,157.7265   $1,157.73   $1,157.75   $1,157.70