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	$158.26	12.220%	$177.5994	$177.60	$177.60	$177.60
Purchase #2	$156.75	10.355%	$172.9815	$172.98	$173.00	$173.00
Purchase #3	$19.37	6.839%	$20.6947	$20.69	$20.70	$20.70
Purchase #4	$82.78	10.649%	$91.5952	$91.60	$91.60	$91.60
Purchase #5	$226.72	7.155%	$242.9418	$242.94	$242.95	$242.90
Purchase #6	$75.80	3.292%	$78.2953	$78.30	$78.30	$78.30
Purchase #7	$46.91	7.707%	$50.5254	$50.53	$50.55	$50.50
7 purchase totals =	$766.59		$834.6333	$834.64	$834.70	$834.60