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	$128.41	5.336%	$135.262	$135.26	$135.25	$135.30
Purchase #2	$112.27	13.170%	$127.056	$127.06	$127.05	$127.10
Purchase #3	$86.28	4.268%	$89.9624	$89.96	$89.95	$90.00
Purchase #4	$139.44	8.363%	$151.1014	$151.10	$151.10	$151.10
Purchase #5	$28.32	10.626%	$31.3293	$31.33	$31.35	$31.30
Purchase #6	$214.37	9.600%	$234.9495	$234.95	$234.95	$234.90
Purchase #7	$215.60	3.739%	$223.6613	$223.66	$223.65	$223.70
7 purchase totals =	$924.69		$993.3219	$993.32	$993.30	$993.40