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 $104.86   8.679%   $113.9608   $113.96   $113.95   $114.00  
  Purchase #2 $134.56   12.630%   $151.5549   $151.55   $151.55   $151.60  
  Purchase #3 $86.33   9.434%   $94.4744   $94.47   $94.45   $94.50  
  Purchase #4 $206.80   8.775%   $224.9467   $224.95   $224.95   $224.90  
  Purchase #5 $8.71   10.789%   $9.6497   $9.65   $9.65   $9.60  
  Purchase #6 $237.27   7.143%   $254.2182   $254.22   $254.20   $254.20  
  Purchase #7 $182.61   12.750%   $205.8928   $205.89   $205.90   $205.90  
  7 purchase totals = $961.14       $1,054.6975   $1,054.69   $1,054.65   $1,054.70