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 $217.40   7.160%   $232.9658   $232.97   $232.95   $233.00  
  Purchase #2 $16.27   3.640%   $16.8622   $16.86   $16.85   $16.90  
  Purchase #3 $117.95   7.576%   $126.8859   $126.89   $126.90   $126.90  
  Purchase #4 $169.40   13.677%   $192.5688   $192.57   $192.55   $192.60  
  Purchase #5 $56.66   8.129%   $61.2659   $61.27   $61.25   $61.30  
  Purchase #6 $250.53   5.667%   $264.7275   $264.73   $264.75   $264.70  
  Purchase #7 $88.36   13.671%   $100.4397   $100.44   $100.45   $100.40  
  7 purchase totals = $916.57       $995.7158   $995.73   $995.70   $995.80