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 $47.33   8.452%   $51.3303   $51.33   $51.35   $51.30  
  Purchase #2 $175.97   12.282%   $197.5826   $197.58   $197.60   $197.60  
  Purchase #3 $72.61   5.800%   $76.8214   $76.82   $76.80   $76.80  
  Purchase #4 $191.62   10.435%   $211.6155   $211.62   $211.60   $211.60  
  Purchase #5 $130.68   4.402%   $136.4325   $136.43   $136.45   $136.40  
  Purchase #6 $116.70   5.350%   $122.9435   $122.94   $122.95   $122.90  
  Purchase #7 $117.95   4.162%   $122.8591   $122.86   $122.85   $122.90  
  7 purchase totals = $852.86       $919.5849   $919.58   $919.60   $919.50