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	$100.32	3.308%	$103.6386	$103.64	$103.65	$103.60
Purchase #2	$216.89	12.616%	$244.2528	$244.25	$244.25	$244.30
Purchase #3	$7.59	3.478%	$7.854	$7.85	$7.85	$7.90
Purchase #4	$44.29	3.277%	$45.7414	$45.74	$45.75	$45.70
Purchase #5	$143.75	6.173%	$152.6237	$152.62	$152.60	$152.60
Purchase #6	$16.43	11.372%	$18.2984	$18.30	$18.30	$18.30
Purchase #7	$212.43	12.198%	$238.3422	$238.34	$238.35	$238.30
7 purchase totals =	$741.70		$810.7511	$810.74	$810.75	$810.70