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 $245.27   6.173%   $260.4105   $260.41   $260.40   $260.40  
  Purchase #2 $154.47   8.669%   $167.861   $167.86   $167.85   $167.90  
  Purchase #3 $15.41   13.820%   $17.5397   $17.54   $17.55   $17.50  
  Purchase #4 $204.72   10.243%   $225.6895   $225.69   $225.70   $225.70  
  Purchase #5 $68.76   7.590%   $73.9789   $73.98   $74.00   $74.00  
  Purchase #6 $161.44   13.323%   $182.9487   $182.95   $182.95   $182.90  
  Purchase #7 $180.44   3.535%   $186.8186   $186.82   $186.80   $186.80  
  7 purchase totals = $1,030.51       $1,115.2469   $1,115.25   $1,115.25   $1,115.20