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 $76.66   8.332%   $83.0473   $83.05   $83.05   $83.00  
  Purchase #2 $115.44   6.808%   $123.2992   $123.30   $123.30   $123.30  
  Purchase #3 $161.86   9.705%   $177.5685   $177.57   $177.55   $177.60  
  Purchase #4 $113.56   7.617%   $122.2099   $122.21   $122.20   $122.20  
  Purchase #5 $56.59   6.305%   $60.158   $60.16   $60.15   $60.20  
  Purchase #6 $111.58   13.250%   $126.3644   $126.36   $126.35   $126.40  
  Purchase #7 $231.65   9.210%   $252.985   $252.99   $253.00   $253.00  
  7 purchase totals = $867.34       $945.6323   $945.64   $945.60   $945.70