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	$213.49	4.638%	$223.3917	$223.39	$223.40	$223.40
Purchase #2	$211.77	8.764%	$230.3295	$230.33	$230.35	$230.30
Purchase #3	$156.58	9.244%	$171.0543	$171.05	$171.05	$171.10
Purchase #4	$70.88	3.426%	$73.3083	$73.31	$73.30	$73.30
Purchase #5	$106.30	11.102%	$118.1014	$118.10	$118.10	$118.10
Purchase #6	$137.91	4.379%	$143.9491	$143.95	$143.95	$143.90
Purchase #7	$132.97	5.272%	$139.9802	$139.98	$140.00	$140.00
7 purchase totals =	$1,029.90		$1,100.1145	$1,100.11	$1,100.15	$1,100.10