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 $239.67   11.406%   $267.0068   $267.01   $267.00   $267.00  
  Purchase #2 $181.37   5.649%   $191.6156   $191.62   $191.60   $191.60  
  Purchase #3 $137.94   8.531%   $149.7077   $149.71   $149.70   $149.70  
  Purchase #4 $150.91   4.634%   $157.9032   $157.90   $157.90   $157.90  
  Purchase #5 $24.71   3.808%   $25.651   $25.65   $25.65   $25.70  
  Purchase #6 $43.92   8.326%   $47.5768   $47.58   $47.60   $47.60  
  Purchase #7 $197.61   6.167%   $209.7966   $209.80   $209.80   $209.80  
  7 purchase totals = $976.13       $1,049.2577   $1,049.27   $1,049.25   $1,049.30