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 $156.85   5.850%   $166.0257   $166.03   $166.05   $166.00  
  Purchase #2 $10.98   7.664%   $11.8215   $11.82   $11.80   $11.80  
  Purchase #3 $48.48   8.249%   $52.4791   $52.48   $52.50   $52.50  
  Purchase #4 $54.27   13.393%   $61.5384   $61.54   $61.55   $61.50  
  Purchase #5 $5.62   6.803%   $6.0023   $6.00   $6.00   $6.00  
  Purchase #6 $214.42   6.527%   $228.4152   $228.42   $228.40   $228.40  
  Purchase #7 $224.36   4.378%   $234.1825   $234.18   $234.20   $234.20  
  7 purchase totals = $714.98       $760.4647   $760.47   $760.50   $760.40