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 $246.32   5.811%   $260.6337   $260.63   $260.65   $260.60  
  Purchase #2 $81.71   3.421%   $84.5053   $84.51   $84.50   $84.50  
  Purchase #3 $49.76   6.542%   $53.0153   $53.02   $53.00   $53.00  
  Purchase #4 $250.71   9.137%   $273.6174   $273.62   $273.60   $273.60  
  Purchase #5 $170.63   7.652%   $183.6866   $183.69   $183.70   $183.70  
  Purchase #6 $243.70   8.555%   $264.5485   $264.55   $264.55   $264.50  
  Purchase #7 $196.94   5.103%   $206.9898   $206.99   $207.00   $207.00  
  7 purchase totals = $1,239.77       $1,326.9966   $1,327.01   $1,327.00   $1,326.90