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 $246.97   10.577%   $273.092   $273.09   $273.10   $273.10  
  Purchase #2 $132.40   10.682%   $146.543   $146.54   $146.55   $146.50  
  Purchase #3 $238.59   7.712%   $256.9901   $256.99   $257.00   $257.00  
  Purchase #4 $85.60   12.853%   $96.6022   $96.60   $96.60   $96.60  
  Purchase #5 $183.49   5.130%   $192.903   $192.90   $192.90   $192.90  
  Purchase #6 $235.32   12.595%   $264.9586   $264.96   $264.95   $265.00  
  Purchase #7 $29.72   5.720%   $31.42   $31.42   $31.40   $31.40  
  7 purchase totals = $1,152.09       $1,262.5089   $1,262.50   $1,262.50   $1,262.50