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	$179.34	3.650%	$185.8859	$185.89	$185.90	$185.90
Purchase #2	$84.33	10.606%	$93.274	$93.27	$93.25	$93.30
Purchase #3	$27.73	11.375%	$30.8843	$30.88	$30.90	$30.90
Purchase #4	$219.94	8.327%	$238.2544	$238.25	$238.25	$238.30
Purchase #5	$138.32	10.866%	$153.3499	$153.35	$153.35	$153.30
Purchase #6	$74.64	5.618%	$78.8333	$78.83	$78.85	$78.80
Purchase #7	$55.27	11.270%	$61.4989	$61.50	$61.50	$61.50
7 purchase totals =	$779.57		$841.9807	$841.97	$842.00	$842.00