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 $250.97   5.676%   $265.2151   $265.22   $265.20   $265.20  
  Purchase #2 $140.88   12.551%   $158.5618   $158.56   $158.55   $158.60  
  Purchase #3 $214.54   11.235%   $238.6436   $238.64   $238.65   $238.60  
  Purchase #4 $44.44   5.611%   $46.9335   $46.93   $46.95   $46.90  
  Purchase #5 $212.35   5.253%   $223.5047   $223.50   $223.50   $223.50  
  Purchase #6 $61.60   5.748%   $65.1408   $65.14   $65.15   $65.10  
  Purchase #7 $121.99   6.232%   $129.5924   $129.59   $129.60   $129.60  
  7 purchase totals = $1,046.77       $1,127.5919   $1,127.58   $1,127.60   $1,127.50