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	$99.94	10.275%	$110.2088	$110.21	$110.20	$110.20
Purchase #2	$214.78	13.366%	$243.4875	$243.49	$243.50	$243.50
Purchase #3	$92.96	13.411%	$105.4269	$105.43	$105.45	$105.40
Purchase #4	$90.46	6.297%	$96.1563	$96.16	$96.15	$96.20
Purchase #5	$166.58	10.594%	$184.2275	$184.23	$184.25	$184.20
Purchase #6	$58.33	11.513%	$65.0455	$65.05	$65.05	$65.00
Purchase #7	$35.93	6.675%	$38.3283	$38.33	$38.35	$38.30
7 purchase totals =	$758.98		$842.8808	$842.90	$842.95	$842.80