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 $85.47   8.571%   $92.7956   $92.80   $92.80   $92.80  
  Purchase #2 $181.70   8.370%   $196.9083   $196.91   $196.90   $196.90  
  Purchase #3 $240.99   4.621%   $252.1261   $252.13   $252.15   $252.10  
  Purchase #4 $14.93   9.615%   $16.3655   $16.37   $16.35   $16.40  
  Purchase #5 $200.75   8.145%   $217.1011   $217.10   $217.10   $217.10  
  Purchase #6 $70.59   4.330%   $73.6465   $73.65   $73.65   $73.60  
  Purchase #7 $163.25   8.674%   $177.4103   $177.41   $177.40   $177.40  
  7 purchase totals = $957.68       $1,026.3534   $1,026.37   $1,026.35   $1,026.30