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 $44.93   6.699%   $47.9399   $47.94   $47.95   $47.90  
  Purchase #2 $180.89   11.514%   $201.7177   $201.72   $201.70   $201.70  
  Purchase #3 $11.52   10.793%   $12.7634   $12.76   $12.75   $12.80  
  Purchase #4 $239.84   11.652%   $267.7862   $267.79   $267.80   $267.80  
  Purchase #5 $124.88   6.349%   $132.8086   $132.81   $132.80   $132.80  
  Purchase #6 $131.67   3.462%   $136.2284   $136.23   $136.25   $136.20  
  Purchase #7 $195.53   5.599%   $206.4777   $206.48   $206.50   $206.50  
  7 purchase totals = $929.26       $1,005.7219   $1,005.73   $1,005.75   $1,005.70