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 $24.65   12.364%   $27.6977   $27.70   $27.70   $27.70  
  Purchase #2 $86.56   11.209%   $96.2625   $96.26   $96.25   $96.30  
  Purchase #3 $242.63   9.722%   $266.2185   $266.22   $266.20   $266.20  
  Purchase #4 $166.75   10.581%   $184.3938   $184.39   $184.40   $184.40  
  Purchase #5 $55.52   8.840%   $60.428   $60.43   $60.45   $60.40  
  Purchase #6 $54.49   13.824%   $62.0227   $62.02   $62.00   $62.00  
  Purchase #7 $144.25   10.337%   $159.1611   $159.16   $159.15   $159.20  
  7 purchase totals = $774.85       $856.1843   $856.18   $856.15   $856.20