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 $249.41   5.618%   $263.4219   $263.42   $263.40   $263.40  
  Purchase #2 $248.25   11.441%   $276.6523   $276.65   $276.65   $276.70  
  Purchase #3 $119.99   11.712%   $134.0432   $134.04   $134.05   $134.00  
  Purchase #4 $116.35   9.579%   $127.4952   $127.50   $127.50   $127.50  
  Purchase #5 $84.84   10.433%   $93.6914   $93.69   $93.70   $93.70  
  Purchase #6 $153.95   8.575%   $167.1512   $167.15   $167.15   $167.20  
  Purchase #7 $36.40   10.250%   $40.131   $40.13   $40.15   $40.10  
  7 purchase totals = $1,009.19       $1,102.5862   $1,102.58   $1,102.60   $1,102.60