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 $98.77   5.463%   $104.1658   $104.17   $104.15   $104.20  
  Purchase #2 $8.35   11.304%   $9.2939   $9.29   $9.30   $9.30  
  Purchase #3 $23.96   11.412%   $26.6943   $26.69   $26.70   $26.70  
  Purchase #4 $5.80   5.655%   $6.128   $6.13   $6.15   $6.10  
  Purchase #5 $119.51   5.391%   $125.9528   $125.95   $125.95   $126.00  
  Purchase #6 $162.34   5.738%   $171.6551   $171.66   $171.65   $171.70  
  Purchase #7 $44.92   8.236%   $48.6196   $48.62   $48.60   $48.60  
  7 purchase totals = $463.65       $492.5095   $492.51   $492.50   $492.60