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 $165.83   11.486%   $184.8772   $184.88   $184.90   $184.90  
  Purchase #2 $137.28   10.232%   $151.3265   $151.33   $151.35   $151.30  
  Purchase #3 $24.62   5.302%   $25.9254   $25.93   $25.95   $25.90  
  Purchase #4 $126.73   3.591%   $131.2809   $131.28   $131.30   $131.30  
  Purchase #5 $111.81   7.819%   $120.5524   $120.55   $120.55   $120.60  
  Purchase #6 $217.49   8.670%   $236.3464   $236.35   $236.35   $236.30  
  Purchase #7 $238.62   12.827%   $269.2278   $269.23   $269.25   $269.20  
  7 purchase totals = $1,022.38       $1,119.5366   $1,119.55   $1,119.65   $1,119.50