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 $162.75   13.371%   $184.5113   $184.51   $184.50   $184.50  
  Purchase #2 $247.60   7.607%   $266.4349   $266.43   $266.45   $266.40  
  Purchase #3 $58.97   9.462%   $64.5497   $64.55   $64.55   $64.50  
  Purchase #4 $168.27   8.626%   $182.785   $182.79   $182.80   $182.80  
  Purchase #5 $61.77   12.814%   $69.6852   $69.69   $69.70   $69.70  
  Purchase #6 $223.76   4.373%   $233.545   $233.55   $233.55   $233.50  
  Purchase #7 $228.62   7.641%   $246.0889   $246.09   $246.10   $246.10  
  7 purchase totals = $1,151.74       $1,247.6000   $1,247.61   $1,247.65   $1,247.50