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 $163.40   10.824%   $181.0864   $181.09   $181.10   $181.10  
  Purchase #2 $173.28   5.846%   $183.4099   $183.41   $183.40   $183.40  
  Purchase #3 $124.33   6.213%   $132.0546   $132.05   $132.05   $132.10  
  Purchase #4 $202.53   11.786%   $226.4002   $226.40   $226.40   $226.40  
  Purchase #5 $29.74   3.252%   $30.7071   $30.71   $30.70   $30.70  
  Purchase #6 $5.73   10.366%   $6.324   $6.32   $6.30   $6.30  
  Purchase #7 $113.99   13.853%   $129.781   $129.78   $129.80   $129.80  
  7 purchase totals = $813.00       $889.7632   $889.76   $889.75   $889.80