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 $162.41   5.561%   $171.4416   $171.44   $171.45   $171.40  
  Purchase #2 $58.67   13.861%   $66.8022   $66.80   $66.80   $66.80  
  Purchase #3 $98.68   8.498%   $107.0658   $107.07   $107.05   $107.10  
  Purchase #4 $22.50   5.697%   $23.7818   $23.78   $23.80   $23.80  
  Purchase #5 $12.67   3.325%   $13.0913   $13.09   $13.10   $13.10  
  Purchase #6 $219.68   10.479%   $242.7003   $242.70   $242.70   $242.70  
  Purchase #7 $67.45   9.253%   $73.6911   $73.69   $73.70   $73.70  
  7 purchase totals = $642.06       $698.5741   $698.57   $698.60   $698.60