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	$173.29	7.621%	$186.4964	$186.50	$186.50	$186.50
Purchase #2	$147.59	10.368%	$162.8921	$162.89	$162.90	$162.90
Purchase #3	$57.98	11.258%	$64.5074	$64.51	$64.50	$64.50
Purchase #4	$140.71	4.660%	$147.2671	$147.27	$147.25	$147.30
Purchase #5	$11.25	4.616%	$11.7693	$11.77	$11.75	$11.80
Purchase #6	$113.62	11.846%	$127.0794	$127.08	$127.10	$127.10
Purchase #7	$158.77	13.696%	$180.5151	$180.52	$180.50	$180.50
7 purchase totals =	$803.21		$880.5268	$880.54	$880.50	$880.60