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 $58.36   5.732%   $61.7052   $61.71   $61.70   $61.70  
  Purchase #2 $210.81   5.625%   $222.6681   $222.67   $222.65   $222.70  
  Purchase #3 $133.93   10.161%   $147.5386   $147.54   $147.55   $147.50  
  Purchase #4 $214.36   5.697%   $226.5721   $226.57   $226.55   $226.60  
  Purchase #5 $175.27   3.502%   $181.408   $181.41   $181.40   $181.40  
  Purchase #6 $14.53   3.147%   $14.9873   $14.99   $15.00   $15.00  
  Purchase #7 $16.25   12.709%   $18.3152   $18.32   $18.30   $18.30  
  7 purchase totals = $823.51       $873.1945   $873.21   $873.15   $873.20