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	$199.80	8.820%	$217.4224	$217.42	$217.40	$217.40
Purchase #2	$173.40	3.316%	$179.1499	$179.15	$179.15	$179.10
Purchase #3	$67.34	8.282%	$72.9171	$72.92	$72.90	$72.90
Purchase #4	$61.85	9.307%	$67.6064	$67.61	$67.60	$67.60
Purchase #5	$171.47	7.246%	$183.8947	$183.89	$183.90	$183.90
Purchase #6	$6.47	13.717%	$7.3575	$7.36	$7.35	$7.40
Purchase #7	$80.29	13.345%	$91.0047	$91.00	$91.00	$91.00
7 purchase totals =	$760.62		$819.3527	$819.35	$819.30	$819.30