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 $108.25   10.693%   $119.8252   $119.83   $119.85   $119.80  
  Purchase #2 $217.87   3.252%   $224.9551   $224.96   $224.95   $225.00  
  Purchase #3 $25.78   9.734%   $28.2894   $28.29   $28.30   $28.30  
  Purchase #4 $136.49   5.649%   $144.2003   $144.20   $144.20   $144.20  
  Purchase #5 $155.25   4.386%   $162.0593   $162.06   $162.05   $162.10  
  Purchase #6 $237.38   3.680%   $246.1156   $246.12   $246.10   $246.10  
  Purchase #7 $79.40   9.479%   $86.9263   $86.93   $86.95   $86.90  
  7 purchase totals = $960.42       $1,012.3712   $1,012.39   $1,012.40   $1,012.40