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 $23.72   10.287%   $26.1601   $26.16   $26.15   $26.20  
  Purchase #2 $72.56   5.739%   $76.7242   $76.72   $76.70   $76.70  
  Purchase #3 $247.26   3.758%   $256.552   $256.55   $256.55   $256.60  
  Purchase #4 $203.27   8.576%   $220.7024   $220.70   $220.70   $220.70  
  Purchase #5 $92.44   6.194%   $98.1657   $98.17   $98.15   $98.20  
  Purchase #6 $246.44   12.332%   $276.831   $276.83   $276.85   $276.80  
  Purchase #7 $212.88   9.219%   $232.5054   $232.51   $232.50   $232.50  
  7 purchase totals = $1,098.57       $1,187.6408   $1,187.64   $1,187.60   $1,187.70