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 $81.69   11.406%   $91.0076   $91.01   $91.00   $91.00  
  Purchase #2 $189.91   8.322%   $205.7143   $205.71   $205.70   $205.70  
  Purchase #3 $126.92   7.786%   $136.802   $136.80   $136.80   $136.80  
  Purchase #4 $215.26   11.462%   $239.9331   $239.93   $239.95   $239.90  
  Purchase #5 $235.86   6.167%   $250.4055   $250.41   $250.40   $250.40  
  Purchase #6 $215.63   4.701%   $225.7668   $225.77   $225.75   $225.80  
  Purchase #7 $112.25   12.205%   $125.9501   $125.95   $125.95   $126.00  
  7 purchase totals = $1,177.52       $1,275.5794   $1,275.58   $1,275.55   $1,275.60