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 $151.95   6.792%   $162.2704   $162.27   $162.25   $162.30  
  Purchase #2 $65.84   11.367%   $73.324   $73.32   $73.30   $73.30  
  Purchase #3 $231.56   8.263%   $250.6938   $250.69   $250.70   $250.70  
  Purchase #4 $75.64   4.812%   $79.2798   $79.28   $79.30   $79.30  
  Purchase #5 $197.47   7.589%   $212.456   $212.46   $212.45   $212.50  
  Purchase #6 $218.86   9.634%   $239.945   $239.95   $239.95   $239.90  
  Purchase #7 $27.25   9.585%   $29.8619   $29.86   $29.85   $29.90  
  7 purchase totals = $968.57       $1,047.8309   $1,047.83   $1,047.80   $1,047.90