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 $186.78   11.711%   $208.6538   $208.65   $208.65   $208.70  
  Purchase #2 $98.38   5.669%   $103.9572   $103.96   $103.95   $104.00  
  Purchase #3 $64.98   7.181%   $69.6462   $69.65   $69.65   $69.60  
  Purchase #4 $163.72   4.867%   $171.6883   $171.69   $171.70   $171.70  
  Purchase #5 $53.35   9.156%   $58.2347   $58.23   $58.25   $58.20  
  Purchase #6 $42.58   11.594%   $47.5167   $47.52   $47.50   $47.50  
  Purchase #7 $118.65   13.361%   $134.5028   $134.50   $134.50   $134.50  
  7 purchase totals = $728.44       $794.1997   $794.20   $794.20   $794.20