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 $56.27   6.541%   $59.9506   $59.95   $59.95   $60.00  
  Purchase #2 $79.91   5.739%   $84.496   $84.50   $84.50   $84.50  
  Purchase #3 $218.33   4.267%   $227.6461   $227.65   $227.65   $227.60  
  Purchase #4 $61.33   10.642%   $67.8567   $67.86   $67.85   $67.90  
  Purchase #5 $187.53   9.345%   $205.0547   $205.05   $205.05   $205.10  
  Purchase #6 $142.49   13.812%   $162.1707   $162.17   $162.15   $162.20  
  Purchase #7 $206.57   7.232%   $221.5091   $221.51   $221.50   $221.50  
  7 purchase totals = $952.43       $1,028.6839   $1,028.69   $1,028.65   $1,028.80