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	$176.97	6.312%	$188.1403	$188.14	$188.15	$188.10
Purchase #2	$29.90	11.146%	$33.2327	$33.23	$33.25	$33.20
Purchase #3	$52.40	13.827%	$59.6453	$59.65	$59.65	$59.60
Purchase #4	$249.54	12.484%	$280.6926	$280.69	$280.70	$280.70
Purchase #5	$146.89	3.276%	$151.7021	$151.70	$151.70	$151.70
Purchase #6	$153.25	6.472%	$163.1683	$163.17	$163.15	$163.20
Purchase #7	$78.36	13.862%	$89.2223	$89.22	$89.20	$89.20
7 purchase totals =	$887.31		$965.8036	$965.80	$965.80	$965.70