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 $67.29   13.831%   $76.5969   $76.60   $76.60   $76.60  
  Purchase #2 $8.31   11.675%   $9.2802   $9.28   $9.30   $9.30  
  Purchase #3 $206.84   3.799%   $214.6979   $214.70   $214.70   $214.70  
  Purchase #4 $242.93   9.696%   $266.4845   $266.48   $266.50   $266.50  
  Purchase #5 $137.28   4.392%   $143.3093   $143.31   $143.30   $143.30  
  Purchase #6 $172.41   7.114%   $184.6752   $184.68   $184.70   $184.70  
  Purchase #7 $122.49   4.328%   $127.7914   $127.79   $127.80   $127.80  
  7 purchase totals = $957.55       $1,022.8354   $1,022.84   $1,022.90   $1,022.90