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	$109.37	6.131%	$116.0755	$116.08	$116.10	$116.10
Purchase #2	$58.76	6.183%	$62.3931	$62.39	$62.40	$62.40
Purchase #3	$247.68	9.469%	$271.1328	$271.13	$271.15	$271.10
Purchase #4	$55.74	12.658%	$62.7956	$62.80	$62.80	$62.80
Purchase #5	$92.78	9.365%	$101.4688	$101.47	$101.45	$101.50
Purchase #6	$34.82	8.538%	$37.7929	$37.79	$37.80	$37.80
Purchase #7	$171.79	5.303%	$180.9	$180.90	$180.90	$180.90
7 purchase totals =	$770.94		$832.5587	$832.56	$832.60	$832.60