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 $46.34   13.841%   $52.7539   $52.75   $52.75   $52.80  
  Purchase #2 $119.30   11.206%   $132.6688   $132.67   $132.65   $132.70  
  Purchase #3 $77.96   11.181%   $86.6767   $86.68   $86.70   $86.70  
  Purchase #4 $142.33   7.259%   $152.6617   $152.66   $152.65   $152.70  
  Purchase #5 $62.80   6.202%   $66.6949   $66.69   $66.70   $66.70  
  Purchase #6 $191.81   3.709%   $198.9242   $198.92   $198.90   $198.90  
  Purchase #7 $151.52   3.843%   $157.3429   $157.34   $157.35   $157.30  
  7 purchase totals = $792.06       $847.7231   $847.71   $847.70   $847.80