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 $232.66   9.577%   $254.9418   $254.94   $254.95   $254.90  
  Purchase #2 $226.25   11.342%   $251.9113   $251.91   $251.90   $251.90  
  Purchase #3 $70.51   6.538%   $75.1199   $75.12   $75.10   $75.10  
  Purchase #4 $239.51   8.336%   $259.4756   $259.48   $259.50   $259.50  
  Purchase #5 $109.42   4.778%   $114.6481   $114.65   $114.65   $114.60  
  Purchase #6 $26.36   6.438%   $28.0571   $28.06   $28.05   $28.10  
  Purchase #7 $213.26   10.467%   $235.5819   $235.58   $235.60   $235.60  
  7 purchase totals = $1,117.97       $1,219.7357   $1,219.74   $1,219.75   $1,219.70