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 $236.87   10.636%   $262.0635   $262.06   $262.05   $262.10  
  Purchase #2 $20.73   7.579%   $22.3011   $22.30   $22.30   $22.30  
  Purchase #3 $69.51   6.572%   $74.0782   $74.08   $74.10   $74.10  
  Purchase #4 $209.41   10.522%   $231.4441   $231.44   $231.45   $231.40  
  Purchase #5 $113.55   6.480%   $120.908   $120.91   $120.90   $120.90  
  Purchase #6 $17.93   8.236%   $19.4067   $19.41   $19.40   $19.40  
  Purchase #7 $147.37   8.714%   $160.2118   $160.21   $160.20   $160.20  
  7 purchase totals = $815.37       $890.4134   $890.41   $890.40   $890.40