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 $64.78   6.458%   $68.9635   $68.96   $68.95   $69.00  
  Purchase #2 $108.59   5.446%   $114.5038   $114.50   $114.50   $114.50  
  Purchase #3 $239.69   12.776%   $270.3128   $270.31   $270.30   $270.30  
  Purchase #4 $165.81   7.744%   $178.6503   $178.65   $178.65   $178.70  
  Purchase #5 $176.50   9.462%   $193.2004   $193.20   $193.20   $193.20  
  Purchase #6 $237.28   11.297%   $264.0855   $264.09   $264.10   $264.10  
  Purchase #7 $243.69   12.280%   $273.6151   $273.62   $273.60   $273.60  
  7 purchase totals = $1,236.34       $1,363.3314   $1,363.33   $1,363.30   $1,363.40