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	$19.75	9.630%	$21.6519	$21.65	$21.65	$21.70
Purchase #2	$61.77	4.303%	$64.428	$64.43	$64.45	$64.40
Purchase #3	$123.83	7.825%	$133.5197	$133.52	$133.50	$133.50
Purchase #4	$44.82	7.165%	$48.0314	$48.03	$48.05	$48.00
Purchase #5	$86.35	11.443%	$96.231	$96.23	$96.25	$96.20
Purchase #6	$231.84	7.103%	$248.3076	$248.31	$248.30	$248.30
Purchase #7	$40.74	3.336%	$42.0991	$42.10	$42.10	$42.10
7 purchase totals =	$609.10		$654.2687	$654.27	$654.30	$654.20