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 $250.77   8.722%   $272.6422   $272.64   $272.65   $272.60  
  Purchase #2 $106.25   13.351%   $120.4354   $120.44   $120.45   $120.40  
  Purchase #3 $12.36   10.558%   $13.665   $13.67   $13.65   $13.70  
  Purchase #4 $71.56   4.229%   $74.5863   $74.59   $74.60   $74.60  
  Purchase #5 $176.86   7.573%   $190.2536   $190.25   $190.25   $190.30  
  Purchase #6 $79.54   9.245%   $86.8935   $86.89   $86.90   $86.90  
  Purchase #7 $61.64   8.288%   $66.7487   $66.75   $66.75   $66.70  
  7 purchase totals = $758.98       $825.2247   $825.23   $825.25   $825.20