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 $235.78   13.817%   $268.3577   $268.36   $268.35   $268.40  
  Purchase #2 $126.64   5.356%   $133.4228   $133.42   $133.40   $133.40  
  Purchase #3 $163.97   7.480%   $176.235   $176.24   $176.25   $176.20  
  Purchase #4 $96.88   13.339%   $109.8028   $109.80   $109.80   $109.80  
  Purchase #5 $107.91   13.641%   $122.63   $122.63   $122.65   $122.60  
  Purchase #6 $52.97   7.412%   $56.8961   $56.90   $56.90   $56.90  
  Purchase #7 $9.65   6.650%   $10.2917   $10.29   $10.30   $10.30  
  7 purchase totals = $793.80       $877.6361   $877.64   $877.65   $877.60