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 $192.53   6.276%   $204.6132   $204.61   $204.60   $204.60  
  Purchase #2 $168.40   11.138%   $187.1564   $187.16   $187.15   $187.20  
  Purchase #3 $180.58   8.743%   $196.3681   $196.37   $196.35   $196.40  
  Purchase #4 $138.62   13.673%   $157.5735   $157.57   $157.55   $157.60  
  Purchase #5 $231.70   13.287%   $262.486   $262.49   $262.50   $262.50  
  Purchase #6 $179.73   11.816%   $200.9669   $200.97   $200.95   $201.00  
  Purchase #7 $67.54   12.533%   $76.0048   $76.00   $76.00   $76.00  
  7 purchase totals = $1,159.10       $1,285.1689   $1,285.17   $1,285.10   $1,285.30