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 $184.88   11.464%   $206.0746   $206.07   $206.05   $206.10  
  Purchase #2 $82.68   11.257%   $91.9873   $91.99   $92.00   $92.00  
  Purchase #3 $31.37   7.455%   $33.7086   $33.71   $33.70   $33.70  
  Purchase #4 $106.81   13.510%   $121.24   $121.24   $121.25   $121.20  
  Purchase #5 $98.56   11.377%   $109.7732   $109.77   $109.75   $109.80  
  Purchase #6 $202.58   5.841%   $214.4127   $214.41   $214.40   $214.40  
  Purchase #7 $165.54   10.416%   $182.7826   $182.78   $182.80   $182.80  
  7 purchase totals = $872.42       $959.9790   $959.97   $959.95   $960.00