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 $78.63   4.245%   $81.9678   $81.97   $81.95   $82.00  
  Purchase #2 $240.68   9.353%   $263.1908   $263.19   $263.20   $263.20  
  Purchase #3 $23.50   5.790%   $24.8607   $24.86   $24.85   $24.90  
  Purchase #4 $184.36   5.147%   $193.849   $193.85   $193.85   $193.80  
  Purchase #5 $198.27   6.161%   $210.4854   $210.49   $210.50   $210.50  
  Purchase #6 $237.67   13.261%   $269.1874   $269.19   $269.20   $269.20  
  Purchase #7 $222.26   8.483%   $241.1143   $241.11   $241.10   $241.10  
  7 purchase totals = $1,185.37       $1,284.6554   $1,284.66   $1,284.65   $1,284.70