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 $227.34   11.230%   $252.8703   $252.87   $252.85   $252.90  
  Purchase #2 $158.82   4.241%   $165.5556   $165.56   $165.55   $165.60  
  Purchase #3 $96.97   12.538%   $109.1281   $109.13   $109.15   $109.10  
  Purchase #4 $40.33   5.477%   $42.5389   $42.54   $42.55   $42.50  
  Purchase #5 $206.52   5.605%   $218.0954   $218.10   $218.10   $218.10  
  Purchase #6 $120.55   11.857%   $134.8436   $134.84   $134.85   $134.80  
  Purchase #7 $47.55   12.718%   $53.5974   $53.60   $53.60   $53.60  
  7 purchase totals = $898.08       $976.6293   $976.64   $976.65   $976.60