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	$72.51	8.851%	$78.9279	$78.93	$78.95	$78.90
Purchase #2	$243.26	12.297%	$273.1737	$273.17	$273.15	$273.20
Purchase #3	$72.58	5.107%	$76.2867	$76.29	$76.30	$76.30
Purchase #4	$48.80	12.303%	$54.8039	$54.80	$54.80	$54.80
Purchase #5	$30.28	6.491%	$32.2455	$32.25	$32.25	$32.20
Purchase #6	$118.97	7.213%	$127.5513	$127.55	$127.55	$127.60
Purchase #7	$165.67	10.489%	$183.0471	$183.05	$183.05	$183.00
7 purchase totals =	$752.07		$826.0361	$826.04	$826.05	$826.00