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 $23.86   13.102%   $26.9861   $26.99   $27.00   $27.00  
  Purchase #2 $231.53   8.486%   $251.1776   $251.18   $251.20   $251.20  
  Purchase #3 $59.45   4.849%   $62.3327   $62.33   $62.35   $62.30  
  Purchase #4 $91.32   13.859%   $103.976   $103.98   $104.00   $104.00  
  Purchase #5 $77.48   6.415%   $82.4503   $82.45   $82.45   $82.50  
  Purchase #6 $212.84   3.608%   $220.5193   $220.52   $220.50   $220.50  
  Purchase #7 $200.52   8.806%   $218.1778   $218.18   $218.20   $218.20  
  7 purchase totals = $897.00       $965.6198   $965.63   $965.70   $965.70