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	$70.51	11.837%	$78.8563	$78.86	$78.85	$78.90
Purchase #2	$212.72	12.852%	$240.0588	$240.06	$240.05	$240.10
Purchase #3	$10.72	7.570%	$11.5315	$11.53	$11.55	$11.50
Purchase #4	$48.25	5.124%	$50.7223	$50.72	$50.70	$50.70
Purchase #5	$209.84	6.358%	$223.1816	$223.18	$223.20	$223.20
Purchase #6	$234.25	10.379%	$258.5628	$258.56	$258.55	$258.60
Purchase #7	$37.66	8.629%	$40.9097	$40.91	$40.90	$40.90
7 purchase totals =	$823.95		$903.8230	$903.82	$903.80	$903.90