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 $87.66   6.248%   $93.137   $93.14   $93.15   $93.10  
  Purchase #2 $115.56   7.850%   $124.6315   $124.63   $124.65   $124.60  
  Purchase #3 $240.70   4.233%   $250.8888   $250.89   $250.90   $250.90  
  Purchase #4 $221.65   8.619%   $240.754   $240.75   $240.75   $240.80  
  Purchase #5 $95.63   5.784%   $101.1612   $101.16   $101.15   $101.20  
  Purchase #6 $16.26   3.862%   $16.888   $16.89   $16.90   $16.90  
  Purchase #7 $152.37   13.395%   $172.78   $172.78   $172.80   $172.80  
  7 purchase totals = $929.83       $1,000.2405   $1,000.24   $1,000.30   $1,000.30