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 $60.49   8.692%   $65.7478   $65.75   $65.75   $65.70  
  Purchase #2 $246.34   11.334%   $274.2602   $274.26   $274.25   $274.30  
  Purchase #3 $148.78   3.589%   $154.1197   $154.12   $154.10   $154.10  
  Purchase #4 $168.88   10.151%   $186.023   $186.02   $186.00   $186.00  
  Purchase #5 $49.98   4.861%   $52.4095   $52.41   $52.40   $52.40  
  Purchase #6 $30.50   4.615%   $31.9076   $31.91   $31.90   $31.90  
  Purchase #7 $218.58   5.782%   $231.2183   $231.22   $231.20   $231.20  
  7 purchase totals = $923.55       $995.6861   $995.69   $995.60   $995.60