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 $206.25   6.195%   $219.0272   $219.03   $219.05   $219.00  
  Purchase #2 $58.83   4.420%   $61.4303   $61.43   $61.45   $61.40  
  Purchase #3 $215.60   6.494%   $229.6011   $229.60   $229.60   $229.60  
  Purchase #4 $203.59   11.345%   $226.6873   $226.69   $226.70   $226.70  
  Purchase #5 $97.41   11.755%   $108.8605   $108.86   $108.85   $108.90  
  Purchase #6 $15.73   6.321%   $16.7243   $16.72   $16.70   $16.70  
  Purchase #7 $104.95   5.317%   $110.5302   $110.53   $110.55   $110.50  
  7 purchase totals = $902.36       $972.8609   $972.86   $972.90   $972.80