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 $88.93   10.462%   $98.2339   $98.23   $98.25   $98.20  
  Purchase #2 $198.48   11.430%   $221.1663   $221.17   $221.15   $221.20  
  Purchase #3 $58.27   4.224%   $60.7313   $60.73   $60.75   $60.70  
  Purchase #4 $214.72   13.625%   $243.9756   $243.98   $244.00   $244.00  
  Purchase #5 $15.55   11.349%   $17.3148   $17.31   $17.30   $17.30  
  Purchase #6 $59.72   13.447%   $67.7505   $67.75   $67.75   $67.80  
  Purchase #7 $61.30   13.308%   $69.4578   $69.46   $69.45   $69.50  
  7 purchase totals = $696.97       $778.6302   $778.63   $778.65   $778.70