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	$137.84	9.767%	$151.3028	$151.30	$151.30	$151.30
Purchase #2	$82.60	9.469%	$90.4214	$90.42	$90.40	$90.40
Purchase #3	$183.62	9.499%	$201.0621	$201.06	$201.05	$201.10
Purchase #4	$219.52	10.644%	$242.8857	$242.89	$242.90	$242.90
Purchase #5	$49.32	3.361%	$50.9776	$50.98	$51.00	$51.00
Purchase #6	$124.31	9.680%	$136.3432	$136.34	$136.35	$136.30
Purchase #7	$249.77	3.428%	$258.3321	$258.33	$258.35	$258.30
7 purchase totals =	$1,046.98		$1,131.3249	$1,131.32	$1,131.35	$1,131.30