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	$28.53	13.591%	$32.4075	$32.41	$32.40	$32.40
Purchase #2	$240.73	11.379%	$268.1227	$268.12	$268.10	$268.10
Purchase #3	$42.53	3.348%	$43.9539	$43.95	$43.95	$44.00
Purchase #4	$230.67	10.478%	$254.8396	$254.84	$254.85	$254.80
Purchase #5	$151.30	8.570%	$164.2664	$164.27	$164.25	$164.30
Purchase #6	$40.41	5.673%	$42.7025	$42.70	$42.70	$42.70
Purchase #7	$83.40	12.716%	$94.0051	$94.01	$94.00	$94.00
7 purchase totals =	$817.57		$900.2977	$900.30	$900.25	$900.30