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	$229.60	8.699%	$249.5729	$249.57	$249.55	$249.60
Purchase #2	$170.63	6.265%	$181.32	$181.32	$181.30	$181.30
Purchase #3	$157.39	11.466%	$175.4363	$175.44	$175.45	$175.40
Purchase #4	$130.47	11.666%	$145.6906	$145.69	$145.70	$145.70
Purchase #5	$219.62	11.688%	$245.2892	$245.29	$245.30	$245.30
Purchase #6	$83.80	6.204%	$88.999	$89.00	$89.00	$89.00
Purchase #7	$166.79	11.301%	$185.6389	$185.64	$185.65	$185.60
7 purchase totals =	$1,158.30		$1,271.9469	$1,271.95	$1,271.95	$1,271.90