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 $104.96   13.711%   $119.3511   $119.35   $119.35   $119.40  
  Purchase #2 $179.60   10.336%   $198.1635   $198.16   $198.15   $198.20  
  Purchase #3 $173.60   3.126%   $179.0267   $179.03   $179.05   $179.00  
  Purchase #4 $246.74   3.796%   $256.1063   $256.11   $256.10   $256.10  
  Purchase #5 $44.69   9.423%   $48.9011   $48.90   $48.90   $48.90  
  Purchase #6 $248.69   12.130%   $278.8561   $278.86   $278.85   $278.90  
  Purchase #7 $193.88   4.673%   $202.94   $202.94   $202.95   $202.90  
  7 purchase totals = $1,192.16       $1,283.3448   $1,283.35   $1,283.35   $1,283.40