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	$174.98	6.201%	$185.8305	$185.83	$185.85	$185.80
Purchase #2	$80.56	12.131%	$90.3327	$90.33	$90.35	$90.30
Purchase #3	$220.41	4.859%	$231.1197	$231.12	$231.10	$231.10
Purchase #4	$165.54	8.771%	$180.0595	$180.06	$180.05	$180.10
Purchase #5	$31.39	3.227%	$32.403	$32.40	$32.40	$32.40
Purchase #6	$98.93	9.395%	$108.2245	$108.22	$108.20	$108.20
Purchase #7	$30.48	9.745%	$33.4503	$33.45	$33.45	$33.50
7 purchase totals =	$802.29		$861.4202	$861.41	$861.40	$861.40