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	$77.38	3.738%	$80.2725	$80.27	$80.25	$80.30
Purchase #2	$79.36	5.623%	$83.8224	$83.82	$83.80	$83.80
Purchase #3	$103.80	5.365%	$109.3689	$109.37	$109.35	$109.40
Purchase #4	$72.89	5.493%	$76.8938	$76.89	$76.90	$76.90
Purchase #5	$72.41	8.222%	$78.3636	$78.36	$78.35	$78.40
Purchase #6	$152.67	10.359%	$168.4851	$168.49	$168.50	$168.50
Purchase #7	$156.36	9.509%	$171.2283	$171.23	$171.25	$171.20
7 purchase totals =	$714.87		$768.4346	$768.43	$768.40	$768.50