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 $236.33   13.243%   $267.6272   $267.63   $267.65   $267.60  
  Purchase #2 $195.82   8.672%   $212.8015   $212.80   $212.80   $212.80  
  Purchase #3 $44.50   5.455%   $46.9275   $46.93   $46.95   $46.90  
  Purchase #4 $107.63   9.578%   $117.9388   $117.94   $117.95   $117.90  
  Purchase #5 $18.39   12.153%   $20.6249   $20.62   $20.60   $20.60  
  Purchase #6 $92.72   6.678%   $98.9118   $98.91   $98.90   $98.90  
  Purchase #7 $92.39   13.107%   $104.4996   $104.50   $104.50   $104.50  
  7 purchase totals = $787.78       $869.3313   $869.33   $869.35   $869.20