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 $88.40   8.486%   $95.9016   $95.90   $95.90   $95.90  
  Purchase #2 $163.97   10.134%   $180.5867   $180.59   $180.60   $180.60  
  Purchase #3 $248.67   9.823%   $273.0969   $273.10   $273.10   $273.10  
  Purchase #4 $83.91   3.414%   $86.7747   $86.77   $86.75   $86.80  
  Purchase #5 $239.69   8.495%   $260.0517   $260.05   $260.05   $260.10  
  Purchase #6 $91.48   4.463%   $95.5628   $95.56   $95.55   $95.60  
  Purchase #7 $29.40   7.299%   $31.5459   $31.55   $31.55   $31.50  
  7 purchase totals = $945.52       $1,023.5203   $1,023.52   $1,023.50   $1,023.60