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	$84.31	7.173%	$90.3576	$90.36	$90.35	$90.40
Purchase #2	$113.47	10.586%	$125.4819	$125.48	$125.50	$125.50
Purchase #3	$85.98	7.373%	$92.3193	$92.32	$92.30	$92.30
Purchase #4	$237.76	5.735%	$251.3955	$251.40	$251.40	$251.40
Purchase #5	$145.56	11.601%	$162.4464	$162.45	$162.45	$162.40
Purchase #6	$9.68	8.254%	$10.479	$10.48	$10.50	$10.50
Purchase #7	$230.78	5.518%	$243.5144	$243.51	$243.50	$243.50
7 purchase totals =	$907.54		$975.9941	$976.00	$976.00	$976.00