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	$83.71	5.780%	$88.5484	$88.55	$88.55	$88.50
Purchase #2	$154.33	10.841%	$171.0609	$171.06	$171.05	$171.10
Purchase #3	$142.88	5.809%	$151.1799	$151.18	$151.20	$151.20
Purchase #4	$206.57	8.251%	$223.6141	$223.61	$223.60	$223.60
Purchase #5	$184.63	11.251%	$205.4027	$205.40	$205.40	$205.40
Purchase #6	$155.56	9.726%	$170.6898	$170.69	$170.70	$170.70
Purchase #7	$141.42	9.190%	$154.4165	$154.42	$154.40	$154.40
7 purchase totals =	$1,069.10		$1,164.9123	$1,164.91	$1,164.90	$1,164.90