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	$152.25	6.653%	$162.3792	$162.38	$162.40	$162.40
Purchase #2	$163.72	13.661%	$186.0858	$186.09	$186.10	$186.10
Purchase #3	$91.74	8.293%	$99.348	$99.35	$99.35	$99.30
Purchase #4	$75.45	10.489%	$83.364	$83.36	$83.35	$83.40
Purchase #5	$164.25	5.204%	$172.7976	$172.80	$172.80	$172.80
Purchase #6	$231.47	8.122%	$250.27	$250.27	$250.25	$250.30
Purchase #7	$228.40	3.173%	$235.6471	$235.65	$235.65	$235.60
7 purchase totals =	$1,107.28		$1,189.8917	$1,189.90	$1,189.90	$1,189.90