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 $58.53   4.766%   $61.3195   $61.32   $61.30   $61.30  
  Purchase #2 $97.35   11.436%   $108.4829   $108.48   $108.50   $108.50  
  Purchase #3 $199.70   9.542%   $218.7554   $218.76   $218.75   $218.80  
  Purchase #4 $218.64   8.375%   $236.9511   $236.95   $236.95   $237.00  
  Purchase #5 $153.88   13.253%   $174.2737   $174.27   $174.25   $174.30  
  Purchase #6 $218.35   12.518%   $245.6831   $245.68   $245.70   $245.70  
  Purchase #7 $222.37   13.699%   $252.8325   $252.83   $252.85   $252.80  
  7 purchase totals = $1,168.82       $1,298.2982   $1,298.29   $1,298.30   $1,298.40