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 $167.39   11.265%   $186.2465   $186.25   $186.25   $186.20  
  Purchase #2 $105.46   5.366%   $111.119   $111.12   $111.10   $111.10  
  Purchase #3 $22.40   11.663%   $25.0125   $25.01   $25.00   $25.00  
  Purchase #4 $244.36   10.248%   $269.402   $269.40   $269.40   $269.40  
  Purchase #5 $206.48   5.652%   $218.1502   $218.15   $218.15   $218.20  
  Purchase #6 $8.85   6.678%   $9.441   $9.44   $9.45   $9.40  
  Purchase #7 $132.32   11.187%   $147.1226   $147.12   $147.10   $147.10  
  7 purchase totals = $887.26       $966.4938   $966.49   $966.45   $966.40