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	$156.66	5.334%	$165.0162	$165.02	$165.00	$165.00
Purchase #2	$113.85	13.486%	$129.2038	$129.20	$129.20	$129.20
Purchase #3	$115.56	10.334%	$127.502	$127.50	$127.50	$127.50
Purchase #4	$17.77	12.799%	$20.0444	$20.04	$20.05	$20.00
Purchase #5	$135.56	12.435%	$152.4169	$152.42	$152.40	$152.40
Purchase #6	$247.61	11.412%	$275.8673	$275.87	$275.85	$275.90
Purchase #7	$72.65	8.540%	$78.8543	$78.85	$78.85	$78.90
7 purchase totals =	$859.66		$948.9049	$948.90	$948.85	$948.90