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 $223.91   11.290%   $249.1894   $249.19   $249.20   $249.20  
  Purchase #2 $173.64   13.643%   $197.3297   $197.33   $197.35   $197.30  
  Purchase #3 $215.57   8.319%   $233.5033   $233.50   $233.50   $233.50  
  Purchase #4 $192.87   10.239%   $212.618   $212.62   $212.60   $212.60  
  Purchase #5 $98.69   10.196%   $108.7524   $108.75   $108.75   $108.80  
  Purchase #6 $62.93   7.501%   $67.6504   $67.65   $67.65   $67.70  
  Purchase #7 $25.59   4.294%   $26.6888   $26.69   $26.70   $26.70  
  7 purchase totals = $993.20       $1,095.7320   $1,095.73   $1,095.75   $1,095.80