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 $223.85   13.488%   $254.0429   $254.04   $254.05   $254.00  
  Purchase #2 $108.34   5.771%   $114.5923   $114.59   $114.60   $114.60  
  Purchase #3 $13.39   11.759%   $14.9645   $14.96   $14.95   $15.00  
  Purchase #4 $194.76   8.705%   $211.7139   $211.71   $211.70   $211.70  
  Purchase #5 $41.59   9.329%   $45.4699   $45.47   $45.45   $45.50  
  Purchase #6 $111.61   5.356%   $117.5878   $117.59   $117.60   $117.60  
  Purchase #7 $8.79   13.414%   $9.9691   $9.97   $9.95   $10.00  
  7 purchase totals = $702.33       $768.3404   $768.33   $768.30   $768.40