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	$97.33	7.319%	$104.4536	$104.45	$104.45	$104.50
Purchase #2	$43.97	3.479%	$45.4997	$45.50	$45.50	$45.50
Purchase #3	$122.59	8.535%	$133.0531	$133.05	$133.05	$133.10
Purchase #4	$103.79	5.850%	$109.8617	$109.86	$109.85	$109.90
Purchase #5	$232.76	13.640%	$264.5085	$264.51	$264.50	$264.50
Purchase #6	$53.30	4.862%	$55.8914	$55.89	$55.90	$55.90
Purchase #7	$102.25	3.597%	$105.9279	$105.93	$105.95	$105.90
7 purchase totals =	$755.99		$819.1959	$819.19	$819.20	$819.30