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 $188.63   9.759%   $207.0384   $207.04   $207.05   $207.00  
  Purchase #2 $140.33   12.745%   $158.2151   $158.22   $158.20   $158.20  
  Purchase #3 $72.85   13.847%   $82.9375   $82.94   $82.95   $82.90  
  Purchase #4 $117.95   11.440%   $131.4435   $131.44   $131.45   $131.40  
  Purchase #5 $201.66   8.113%   $218.0207   $218.02   $218.00   $218.00  
  Purchase #6 $250.81   11.517%   $279.6958   $279.70   $279.70   $279.70  
  Purchase #7 $154.32   8.811%   $167.9171   $167.92   $167.90   $167.90  
  7 purchase totals = $1,126.55       $1,245.2681   $1,245.28   $1,245.25   $1,245.10