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 $29.63   8.194%   $32.0579   $32.06   $32.05   $32.10  
  Purchase #2 $148.69   9.609%   $162.9776   $162.98   $163.00   $163.00  
  Purchase #3 $215.81   6.374%   $229.5657   $229.57   $229.55   $229.60  
  Purchase #4 $233.53   3.192%   $240.9843   $240.98   $241.00   $241.00  
  Purchase #5 $249.76   6.307%   $265.5124   $265.51   $265.50   $265.50  
  Purchase #6 $203.84   10.346%   $224.9293   $224.93   $224.95   $224.90  
  Purchase #7 $214.47   10.241%   $236.4339   $236.43   $236.45   $236.40  
  7 purchase totals = $1,295.73       $1,392.4611   $1,392.46   $1,392.50   $1,392.50