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 $60.99   3.421%   $63.0765   $63.08   $63.10   $63.10  
  Purchase #2 $237.91   10.527%   $262.9548   $262.95   $262.95   $263.00  
  Purchase #3 $225.72   7.702%   $243.105   $243.11   $243.10   $243.10  
  Purchase #4 $119.29   12.558%   $134.2704   $134.27   $134.25   $134.30  
  Purchase #5 $79.36   6.254%   $84.3232   $84.32   $84.30   $84.30  
  Purchase #6 $156.71   7.382%   $168.2783   $168.28   $168.30   $168.30  
  Purchase #7 $125.99   5.168%   $132.5012   $132.50   $132.50   $132.50  
  7 purchase totals = $1,005.97       $1,088.5094   $1,088.51   $1,088.50   $1,088.60