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 $96.46   6.795%   $103.0145   $103.01   $103.00   $103.00  
  Purchase #2 $91.27   5.191%   $96.0078   $96.01   $96.00   $96.00  
  Purchase #3 $178.62   8.382%   $193.5919   $193.59   $193.60   $193.60  
  Purchase #4 $141.77   4.375%   $147.9724   $147.97   $147.95   $148.00  
  Purchase #5 $167.93   6.555%   $178.9378   $178.94   $178.95   $178.90  
  Purchase #6 $108.94   5.106%   $114.5025   $114.50   $114.50   $114.50  
  Purchase #7 $45.64   8.216%   $49.3898   $49.39   $49.40   $49.40  
  7 purchase totals = $830.63       $883.4167   $883.41   $883.40   $883.40