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 $136.52   12.466%   $153.5386   $153.54   $153.55   $153.50  
  Purchase #2 $175.77   6.713%   $187.5694   $187.57   $187.55   $187.60  
  Purchase #3 $84.84   11.863%   $94.9046   $94.90   $94.90   $94.90  
  Purchase #4 $238.82   5.745%   $252.5402   $252.54   $252.55   $252.50  
  Purchase #5 $81.95   5.215%   $86.2237   $86.22   $86.20   $86.20  
  Purchase #6 $206.72   5.410%   $217.9036   $217.90   $217.90   $217.90  
  Purchase #7 $246.37   6.503%   $262.3914   $262.39   $262.40   $262.40  
  7 purchase totals = $1,170.99       $1,255.0715   $1,255.06   $1,255.05   $1,255.00