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 $216.46   4.788%   $226.8241   $226.82   $226.80   $226.80  
  Purchase #2 $161.38   11.837%   $180.4826   $180.48   $180.50   $180.50  
  Purchase #3 $33.48   11.526%   $37.3389   $37.34   $37.35   $37.30  
  Purchase #4 $240.85   5.799%   $254.8169   $254.82   $254.80   $254.80  
  Purchase #5 $232.44   12.874%   $262.3643   $262.36   $262.35   $262.40  
  Purchase #6 $71.65   11.555%   $79.9292   $79.93   $79.95   $79.90  
  Purchase #7 $16.88   12.215%   $18.9419   $18.94   $18.95   $18.90  
  7 purchase totals = $973.14       $1,060.6979   $1,060.69   $1,060.70   $1,060.60