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 $101.60   3.521%   $105.1773   $105.18   $105.20   $105.20  
  Purchase #2 $171.56   11.720%   $191.6668   $191.67   $191.65   $191.70  
  Purchase #3 $219.76   3.367%   $227.1593   $227.16   $227.15   $227.20  
  Purchase #4 $144.71   4.662%   $151.4564   $151.46   $151.45   $151.50  
  Purchase #5 $52.62   11.547%   $58.696   $58.70   $58.70   $58.70  
  Purchase #6 $220.39   5.509%   $232.5313   $232.53   $232.55   $232.50  
  Purchase #7 $51.91   11.414%   $57.835   $57.84   $57.85   $57.80  
  7 purchase totals = $962.55       $1,024.5221   $1,024.54   $1,024.55   $1,024.60