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 $162.93   3.709%   $168.9731   $168.97   $168.95   $169.00  
  Purchase #2 $230.69   13.586%   $262.0315   $262.03   $262.05   $262.00  
  Purchase #3 $31.33   8.621%   $34.031   $34.03   $34.05   $34.00  
  Purchase #4 $244.39   6.458%   $260.1727   $260.17   $260.15   $260.20  
  Purchase #5 $115.95   13.288%   $131.3574   $131.36   $131.35   $131.40  
  Purchase #6 $53.43   9.465%   $58.4871   $58.49   $58.50   $58.50  
  Purchase #7 $48.26   3.338%   $49.8709   $49.87   $49.85   $49.90  
  7 purchase totals = $886.98       $964.9237   $964.92   $964.90   $965.00