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 $61.81   5.184%   $65.0142   $65.01   $65.00   $65.00  
  Purchase #2 $188.41   3.473%   $194.9535   $194.95   $194.95   $195.00  
  Purchase #3 $159.62   9.772%   $175.2181   $175.22   $175.20   $175.20  
  Purchase #4 $230.84   10.648%   $255.4198   $255.42   $255.40   $255.40  
  Purchase #5 $87.99   3.684%   $91.2316   $91.23   $91.25   $91.20  
  Purchase #6 $241.86   4.477%   $252.6881   $252.69   $252.70   $252.70  
  Purchase #7 $58.77   10.840%   $65.1407   $65.14   $65.15   $65.10  
  7 purchase totals = $1,029.30       $1,099.6660   $1,099.66   $1,099.65   $1,099.60