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 $250.45   6.220%   $266.028   $266.03   $266.05   $266.00  
  Purchase #2 $152.63   4.580%   $159.6205   $159.62   $159.60   $159.60  
  Purchase #3 $187.85   6.632%   $200.3082   $200.31   $200.30   $200.30  
  Purchase #4 $192.83   11.373%   $214.7606   $214.76   $214.75   $214.80  
  Purchase #5 $7.30   3.153%   $7.5302   $7.53   $7.55   $7.50  
  Purchase #6 $53.54   7.809%   $57.7209   $57.72   $57.70   $57.70  
  Purchase #7 $236.25   4.526%   $246.9427   $246.94   $246.95   $246.90  
  7 purchase totals = $1,080.85       $1,152.9111   $1,152.91   $1,152.90   $1,152.80