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 $234.76   13.412%   $266.246   $266.25   $266.25   $266.20  
  Purchase #2 $229.76   8.545%   $249.393   $249.39   $249.40   $249.40  
  Purchase #3 $250.32   9.538%   $274.1955   $274.20   $274.20   $274.20  
  Purchase #4 $41.52   4.237%   $43.2792   $43.28   $43.30   $43.30  
  Purchase #5 $24.92   8.654%   $27.0766   $27.08   $27.10   $27.10  
  Purchase #6 $40.27   3.420%   $41.6472   $41.65   $41.65   $41.60  
  Purchase #7 $163.50   7.562%   $175.8639   $175.86   $175.85   $175.90  
  7 purchase totals = $985.05       $1,077.7014   $1,077.71   $1,077.75   $1,077.70