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	$127.85	11.656%	$142.7522	$142.75	$142.75	$142.80
Purchase #2	$207.96	10.560%	$229.9206	$229.92	$229.90	$229.90
Purchase #3	$41.89	10.325%	$46.2151	$46.22	$46.20	$46.20
Purchase #4	$46.55	8.649%	$50.5761	$50.58	$50.60	$50.60
Purchase #5	$197.77	5.683%	$209.0093	$209.01	$209.00	$209.00
Purchase #6	$23.36	4.683%	$24.4539	$24.45	$24.45	$24.50
Purchase #7	$123.28	3.346%	$127.4049	$127.40	$127.40	$127.40
7 purchase totals =	$768.66		$830.3321	$830.33	$830.30	$830.40