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 $64.30   3.464%   $66.5274   $66.53   $66.55   $66.50  
  Purchase #2 $239.99   3.687%   $248.8384   $248.84   $248.85   $248.80  
  Purchase #3 $85.82   11.285%   $95.5048   $95.50   $95.50   $95.50  
  Purchase #4 $189.69   5.249%   $199.6468   $199.65   $199.65   $199.60  
  Purchase #5 $101.36   12.806%   $114.3402   $114.34   $114.35   $114.30  
  Purchase #6 $14.49   10.434%   $16.0019   $16.00   $16.00   $16.00  
  Purchase #7 $91.76   3.603%   $95.0661   $95.07   $95.05   $95.10  
  7 purchase totals = $787.41       $835.9256   $835.93   $835.95   $835.80