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 $104.73   6.606%   $111.6485   $111.65   $111.65   $111.60  
  Purchase #2 $211.62   10.461%   $233.7576   $233.76   $233.75   $233.80  
  Purchase #3 $98.88   11.286%   $110.0396   $110.04   $110.05   $110.00  
  Purchase #4 $141.30   4.374%   $147.4805   $147.48   $147.50   $147.50  
  Purchase #5 $66.45   3.309%   $68.6488   $68.65   $68.65   $68.60  
  Purchase #6 $233.55   12.582%   $262.9353   $262.94   $262.95   $262.90  
  Purchase #7 $162.86   6.458%   $173.3775   $173.38   $173.40   $173.40  
  7 purchase totals = $1,019.39       $1,107.8878   $1,107.90   $1,107.95   $1,107.80