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 $63.69   7.737%   $68.6177   $68.62   $68.60   $68.60  
  Purchase #2 $106.26   5.524%   $112.1298   $112.13   $112.15   $112.10  
  Purchase #3 $249.65   3.591%   $258.6149   $258.61   $258.60   $258.60  
  Purchase #4 $150.60   7.781%   $162.3182   $162.32   $162.30   $162.30  
  Purchase #5 $166.78   8.555%   $181.048   $181.05   $181.05   $181.00  
  Purchase #6 $238.88   13.611%   $271.394   $271.39   $271.40   $271.40  
  Purchase #7 $187.93   13.780%   $213.8268   $213.83   $213.85   $213.80  
  7 purchase totals = $1,163.79       $1,267.9494   $1,267.95   $1,267.95   $1,267.80