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	$89.35	11.587%	$99.703	$99.70	$99.70	$99.70
Purchase #2	$79.69	4.108%	$82.9637	$82.96	$82.95	$83.00
Purchase #3	$156.96	10.364%	$173.2273	$173.23	$173.25	$173.20
Purchase #4	$54.91	6.343%	$58.3929	$58.39	$58.40	$58.40
Purchase #5	$89.29	7.705%	$96.1698	$96.17	$96.15	$96.20
Purchase #6	$243.62	6.863%	$260.3396	$260.34	$260.35	$260.30
Purchase #7	$222.73	11.136%	$247.5332	$247.53	$247.55	$247.50
7 purchase totals =	$936.55		$1,018.3295	$1,018.32	$1,018.35	$1,018.30