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 $64.59   4.201%   $67.3034   $67.30   $67.30   $67.30  
  Purchase #2 $245.78   11.385%   $273.7621   $273.76   $273.75   $273.80  
  Purchase #3 $133.68   10.146%   $147.2432   $147.24   $147.25   $147.20  
  Purchase #4 $63.30   5.189%   $66.5846   $66.58   $66.60   $66.60  
  Purchase #5 $227.28   9.547%   $248.9784   $248.98   $249.00   $249.00  
  Purchase #6 $62.98   8.539%   $68.3579   $68.36   $68.35   $68.40  
  Purchase #7 $174.84   4.202%   $182.1868   $182.19   $182.20   $182.20  
  7 purchase totals = $972.45       $1,054.4164   $1,054.41   $1,054.45   $1,054.50