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	$137.30	7.187%	$147.1678	$147.17	$147.15	$147.20
Purchase #2	$70.49	11.519%	$78.6097	$78.61	$78.60	$78.60
Purchase #3	$116.95	8.788%	$127.2276	$127.23	$127.25	$127.20
Purchase #4	$52.30	8.813%	$56.9092	$56.91	$56.90	$56.90
Purchase #5	$237.41	6.837%	$253.6417	$253.64	$253.65	$253.60
Purchase #6	$54.30	5.636%	$57.3603	$57.36	$57.35	$57.40
Purchase #7	$102.51	11.106%	$113.8948	$113.89	$113.90	$113.90
7 purchase totals =	$771.26		$834.8111	$834.81	$834.80	$834.80