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 $225.41   9.147%   $246.0283   $246.03   $246.05   $246.00  
  Purchase #2 $208.55   13.164%   $236.0035   $236.00   $236.00   $236.00  
  Purchase #3 $136.70   13.281%   $154.8551   $154.86   $154.85   $154.90  
  Purchase #4 $31.69   5.153%   $33.323   $33.32   $33.30   $33.30  
  Purchase #5 $72.89   5.798%   $77.1162   $77.12   $77.10   $77.10  
  Purchase #6 $169.26   11.114%   $188.0716   $188.07   $188.05   $188.10  
  Purchase #7 $43.86   11.854%   $49.0592   $49.06   $49.05   $49.10  
  7 purchase totals = $888.36       $984.4569   $984.46   $984.40   $984.50