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	$170.58	10.774%	$188.9583	$188.96	$188.95	$189.00
Purchase #2	$158.74	4.210%	$165.423	$165.42	$165.40	$165.40
Purchase #3	$154.67	6.173%	$164.2178	$164.22	$164.20	$164.20
Purchase #4	$154.86	10.763%	$171.5276	$171.53	$171.55	$171.50
Purchase #5	$73.44	12.129%	$82.3475	$82.35	$82.35	$82.30
Purchase #6	$121.26	13.244%	$137.3197	$137.32	$137.30	$137.30
Purchase #7	$133.92	13.368%	$151.8224	$151.82	$151.80	$151.80
7 purchase totals =	$967.47		$1,061.6163	$1,061.62	$1,061.55	$1,061.50