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 $53.95   12.428%   $60.6549   $60.65   $60.65   $60.70  
  Purchase #2 $224.42   9.683%   $246.1506   $246.15   $246.15   $246.20  
  Purchase #3 $67.72   5.787%   $71.639   $71.64   $71.65   $71.60  
  Purchase #4 $115.57   10.358%   $127.5407   $127.54   $127.55   $127.50  
  Purchase #5 $29.85   6.569%   $31.8108   $31.81   $31.80   $31.80  
  Purchase #6 $229.82   4.348%   $239.8126   $239.81   $239.80   $239.80  
  Purchase #7 $37.59   6.849%   $40.1645   $40.16   $40.15   $40.20  
  7 purchase totals = $758.92       $817.7731   $817.76   $817.75   $817.80