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 $49.27   8.245%   $53.3323   $53.33   $53.35   $53.30  
  Purchase #2 $122.41   7.229%   $131.259   $131.26   $131.25   $131.30  
  Purchase #3 $33.36   12.163%   $37.4176   $37.42   $37.40   $37.40  
  Purchase #4 $208.66   12.471%   $234.682   $234.68   $234.70   $234.70  
  Purchase #5 $209.39   13.836%   $238.3612   $238.36   $238.35   $238.40  
  Purchase #6 $151.29   3.255%   $156.2145   $156.21   $156.20   $156.20  
  Purchase #7 $28.80   6.686%   $30.7256   $30.73   $30.75   $30.70  
  7 purchase totals = $803.18       $881.9922   $881.99   $882.00   $882.00