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 $67.72   8.292%   $73.3353   $73.34   $73.35   $73.30  
  Purchase #2 $222.63   10.493%   $245.9906   $245.99   $246.00   $246.00  
  Purchase #3 $20.56   10.283%   $22.6742   $22.67   $22.65   $22.70  
  Purchase #4 $217.41   6.544%   $231.6373   $231.64   $231.65   $231.60  
  Purchase #5 $19.70   10.584%   $21.785   $21.79   $21.80   $21.80  
  Purchase #6 $228.47   11.560%   $254.8811   $254.88   $254.90   $254.90  
  Purchase #7 $32.32   10.181%   $35.6105   $35.61   $35.60   $35.60  
  7 purchase totals = $808.81       $885.9140   $885.92   $885.95   $885.90