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	$248.37	9.525%	$272.0272	$272.03	$272.05	$272.00
Purchase #2	$85.66	6.114%	$90.8973	$90.90	$90.90	$90.90
Purchase #3	$105.26	8.755%	$114.4755	$114.48	$114.50	$114.50
Purchase #4	$90.55	8.597%	$98.3346	$98.33	$98.35	$98.30
Purchase #5	$88.53	10.396%	$97.7336	$97.73	$97.75	$97.70
Purchase #6	$197.72	6.145%	$209.8699	$209.87	$209.85	$209.90
Purchase #7	$174.58	7.616%	$187.876	$187.88	$187.90	$187.90
7 purchase totals =	$990.67		$1,071.2141	$1,071.22	$1,071.30	$1,071.20