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 $24.53   3.580%   $25.4082   $25.41   $25.40   $25.40  
  Purchase #2 $215.35   5.267%   $226.6925   $226.69   $226.70   $226.70  
  Purchase #3 $5.58   7.384%   $5.992   $5.99   $6.00   $6.00  
  Purchase #4 $121.36   10.565%   $134.1817   $134.18   $134.20   $134.20  
  Purchase #5 $243.78   3.783%   $253.0022   $253.00   $253.00   $253.00  
  Purchase #6 $244.75   12.774%   $276.0144   $276.01   $276.00   $276.00  
  Purchase #7 $160.90   13.728%   $182.9884   $182.99   $183.00   $183.00  
  7 purchase totals = $1,016.25       $1,104.2794   $1,104.27   $1,104.30   $1,104.30