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	$47.52	11.478%	$52.9743	$52.97	$52.95	$53.00
Purchase #2	$116.36	6.280%	$123.6674	$123.67	$123.65	$123.70
Purchase #3	$179.30	8.410%	$194.3791	$194.38	$194.40	$194.40
Purchase #4	$38.98	3.836%	$40.4753	$40.48	$40.50	$40.50
Purchase #5	$65.27	8.572%	$70.8649	$70.86	$70.85	$70.90
Purchase #6	$35.80	5.608%	$37.8077	$37.81	$37.80	$37.80
Purchase #7	$122.63	13.505%	$139.1912	$139.19	$139.20	$139.20
7 purchase totals =	$605.86		$659.3599	$659.36	$659.35	$659.50