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	$14.93	5.683%	$15.7785	$15.78	$15.80	$15.80
Purchase #2	$135.78	3.788%	$140.9233	$140.92	$140.90	$140.90
Purchase #3	$105.84	6.447%	$112.6635	$112.66	$112.65	$112.70
Purchase #4	$130.27	9.326%	$142.419	$142.42	$142.40	$142.40
Purchase #5	$186.78	4.250%	$194.7182	$194.72	$194.70	$194.70
Purchase #6	$190.56	10.214%	$210.0238	$210.02	$210.00	$210.00
Purchase #7	$57.63	3.374%	$59.5744	$59.57	$59.55	$59.60
7 purchase totals =	$821.79		$876.1007	$876.09	$876.00	$876.10