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 $67.64   13.614%   $76.8485   $76.85   $76.85   $76.80  
  Purchase #2 $128.98   3.397%   $133.3615   $133.36   $133.35   $133.40  
  Purchase #3 $107.56   6.641%   $114.7031   $114.70   $114.70   $114.70  
  Purchase #4 $172.50   7.707%   $185.7946   $185.79   $185.80   $185.80  
  Purchase #5 $216.90   11.340%   $241.4965   $241.50   $241.50   $241.50  
  Purchase #6 $72.68   4.381%   $75.8641   $75.86   $75.85   $75.90  
  Purchase #7 $64.35   7.326%   $69.0643   $69.06   $69.05   $69.10  
  7 purchase totals = $830.61       $897.1326   $897.12   $897.10   $897.20