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 $246.52   3.832%   $255.9666   $255.97   $255.95   $256.00  
  Purchase #2 $151.28   4.448%   $158.0089   $158.01   $158.00   $158.00  
  Purchase #3 $240.93   8.493%   $261.3922   $261.39   $261.40   $261.40  
  Purchase #4 $66.62   6.351%   $70.851   $70.85   $70.85   $70.90  
  Purchase #5 $186.54   8.509%   $202.4127   $202.41   $202.40   $202.40  
  Purchase #6 $165.26   7.507%   $177.6661   $177.67   $177.65   $177.70  
  Purchase #7 $63.90   7.570%   $68.7372   $68.74   $68.75   $68.70  
  7 purchase totals = $1,121.05       $1,195.0347   $1,195.04   $1,195.00   $1,195.10