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	$34.45	8.312%	$37.3135	$37.31	$37.30	$37.30
Purchase #2	$17.59	8.850%	$19.1467	$19.15	$19.15	$19.10
Purchase #3	$149.61	3.619%	$155.0244	$155.02	$155.00	$155.00
Purchase #4	$212.46	12.460%	$238.9325	$238.93	$238.95	$238.90
Purchase #5	$215.50	6.523%	$229.5571	$229.56	$229.55	$229.60
Purchase #6	$20.38	10.233%	$22.4655	$22.47	$22.45	$22.50
Purchase #7	$219.31	13.758%	$249.4827	$249.48	$249.50	$249.50
7 purchase totals =	$869.30		$951.9224	$951.92	$951.90	$951.90