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 $24.34   6.712%   $25.9737   $25.97   $25.95   $26.00  
  Purchase #2 $123.84   12.598%   $139.4414   $139.44   $139.45   $139.40  
  Purchase #3 $154.77   4.685%   $162.021   $162.02   $162.00   $162.00  
  Purchase #4 $170.84   12.587%   $192.3436   $192.34   $192.35   $192.30  
  Purchase #5 $232.97   7.184%   $249.7066   $249.71   $249.70   $249.70  
  Purchase #6 $62.50   7.497%   $67.1856   $67.19   $67.20   $67.20  
  Purchase #7 $179.50   11.627%   $200.3705   $200.37   $200.35   $200.40  
  7 purchase totals = $948.76       $1,037.0424   $1,037.04   $1,037.00   $1,037.00