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 $246.83   11.486%   $275.1809   $275.18   $275.20   $275.20  
  Purchase #2 $54.46   3.659%   $56.4527   $56.45   $56.45   $56.50  
  Purchase #3 $161.27   4.848%   $169.0884   $169.09   $169.10   $169.10  
  Purchase #4 $197.57   12.208%   $221.6893   $221.69   $221.70   $221.70  
  Purchase #5 $157.79   11.638%   $176.1536   $176.15   $176.15   $176.20  
  Purchase #6 $223.31   7.449%   $239.9444   $239.94   $239.95   $239.90  
  Purchase #7 $35.56   5.687%   $37.5823   $37.58   $37.60   $37.60  
  7 purchase totals = $1,076.79       $1,176.0916   $1,176.08   $1,176.15   $1,176.20