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 $246.38   7.216%   $264.1588   $264.16   $264.15   $264.20  
  Purchase #2 $85.54   8.323%   $92.6595   $92.66   $92.65   $92.70  
  Purchase #3 $56.80   7.355%   $60.9776   $60.98   $61.00   $61.00  
  Purchase #4 $14.70   3.365%   $15.1947   $15.19   $15.20   $15.20  
  Purchase #5 $100.79   13.439%   $114.3352   $114.34   $114.35   $114.30  
  Purchase #6 $214.66   13.366%   $243.3515   $243.35   $243.35   $243.40  
  Purchase #7 $51.85   12.852%   $58.5138   $58.51   $58.50   $58.50  
  7 purchase totals = $770.72       $849.1911   $849.19   $849.20   $849.30