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 $207.25   12.836%   $233.8526   $233.85   $233.85   $233.90  
  Purchase #2 $191.54   6.864%   $204.6873   $204.69   $204.70   $204.70  
  Purchase #3 $132.26   11.595%   $147.5955   $147.60   $147.60   $147.60  
  Purchase #4 $76.39   4.324%   $79.6931   $79.69   $79.70   $79.70  
  Purchase #5 $162.45   7.459%   $174.5671   $174.57   $174.55   $174.60  
  Purchase #6 $5.48   10.229%   $6.0405   $6.04   $6.05   $6.00  
  Purchase #7 $57.45   5.323%   $60.5081   $60.51   $60.50   $60.50  
  7 purchase totals = $832.82       $906.9442   $906.95   $906.95   $907.00