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	$167.45	3.417%	$173.1718	$173.17	$173.15	$173.20
Purchase #2	$39.82	7.186%	$42.6815	$42.68	$42.70	$42.70
Purchase #3	$210.34	6.160%	$223.2969	$223.30	$223.30	$223.30
Purchase #4	$90.80	6.459%	$96.6648	$96.66	$96.65	$96.70
Purchase #5	$137.93	9.335%	$150.8058	$150.81	$150.80	$150.80
Purchase #6	$70.81	10.809%	$78.4639	$78.46	$78.45	$78.50
Purchase #7	$110.95	8.217%	$120.0668	$120.07	$120.05	$120.10
7 purchase totals =	$828.10		$885.1515	$885.15	$885.10	$885.30