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 $57.49   6.115%   $61.0055   $61.01   $61.00   $61.00  
  Purchase #2 $55.93   6.638%   $59.6426   $59.64   $59.65   $59.60  
  Purchase #3 $185.47   11.126%   $206.1054   $206.11   $206.10   $206.10  
  Purchase #4 $226.35   11.159%   $251.6084   $251.61   $251.60   $251.60  
  Purchase #5 $121.83   9.170%   $133.0018   $133.00   $133.00   $133.00  
  Purchase #6 $190.64   4.522%   $199.2607   $199.26   $199.25   $199.30  
  Purchase #7 $64.94   12.411%   $72.9997   $73.00   $73.00   $73.00  
  7 purchase totals = $902.65       $983.6241   $983.63   $983.60   $983.60