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 $226.78   4.817%   $237.704   $237.70   $237.70   $237.70  
  Purchase #2 $241.96   4.676%   $253.274   $253.27   $253.25   $253.30  
  Purchase #3 $35.80   7.673%   $38.5469   $38.55   $38.55   $38.50  
  Purchase #4 $14.38   5.860%   $15.2227   $15.22   $15.20   $15.20  
  Purchase #5 $89.61   7.385%   $96.2277   $96.23   $96.25   $96.20  
  Purchase #6 $179.63   3.171%   $185.3261   $185.33   $185.35   $185.30  
  Purchase #7 $210.92   12.315%   $236.8948   $236.89   $236.90   $236.90  
  7 purchase totals = $999.08       $1,063.1962   $1,063.19   $1,063.20   $1,063.10