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 $156.89   5.818%   $166.0179   $166.02   $166.00   $166.00  
  Purchase #2 $10.36   12.521%   $11.6572   $11.66   $11.65   $11.70  
  Purchase #3 $136.67   13.597%   $155.253   $155.25   $155.25   $155.30  
  Purchase #4 $33.65   6.763%   $35.9257   $35.93   $35.95   $35.90  
  Purchase #5 $221.84   6.642%   $236.5746   $236.57   $236.55   $236.60  
  Purchase #6 $187.97   10.623%   $207.9381   $207.94   $207.95   $207.90  
  Purchase #7 $126.57   9.423%   $138.4967   $138.50   $138.50   $138.50  
  7 purchase totals = $873.95       $951.8632   $951.87   $951.85   $951.90