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 $25.27   6.218%   $26.8413   $26.84   $26.85   $26.80  
  Purchase #2 $167.53   11.844%   $187.3723   $187.37   $187.35   $187.40  
  Purchase #3 $184.71   6.418%   $196.5647   $196.56   $196.55   $196.60  
  Purchase #4 $95.62   11.407%   $106.5274   $106.53   $106.55   $106.50  
  Purchase #5 $191.30   4.769%   $200.4231   $200.42   $200.40   $200.40  
  Purchase #6 $211.34   13.374%   $239.6046   $239.60   $239.60   $239.60  
  Purchase #7 $197.45   5.342%   $207.9978   $208.00   $208.00   $208.00  
  7 purchase totals = $1,073.22       $1,165.3312   $1,165.32   $1,165.30   $1,165.30