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 $174.83   10.777%   $193.6714   $193.67   $193.65   $193.70  
  Purchase #2 $205.96   9.726%   $225.9917   $225.99   $226.00   $226.00  
  Purchase #3 $158.85   7.537%   $170.8225   $170.82   $170.80   $170.80  
  Purchase #4 $35.92   12.419%   $40.3809   $40.38   $40.40   $40.40  
  Purchase #5 $151.91   10.740%   $168.2251   $168.23   $168.25   $168.20  
  Purchase #6 $66.93   4.333%   $69.8301   $69.83   $69.85   $69.80  
  Purchase #7 $226.68   4.499%   $236.8783   $236.88   $236.90   $236.90  
  7 purchase totals = $1,021.08       $1,105.8000   $1,105.80   $1,105.85   $1,105.80