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 $250.59   7.324%   $268.9432   $268.94   $268.95   $268.90  
  Purchase #2 $64.41   12.779%   $72.641   $72.64   $72.65   $72.60  
  Purchase #3 $239.29   3.522%   $247.7178   $247.72   $247.70   $247.70  
  Purchase #4 $224.34   5.830%   $237.419   $237.42   $237.40   $237.40  
  Purchase #5 $187.61   3.196%   $193.606   $193.61   $193.60   $193.60  
  Purchase #6 $242.44   11.782%   $271.0043   $271.00   $271.00   $271.00  
  Purchase #7 $60.91   5.841%   $64.4678   $64.47   $64.45   $64.50  
  7 purchase totals = $1,269.59       $1,355.7991   $1,355.80   $1,355.75   $1,355.70