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	$99.80	3.112%	$102.9058	$102.91	$102.90	$102.90
Purchase #2	$70.31	10.720%	$77.8472	$77.85	$77.85	$77.80
Purchase #3	$153.75	13.362%	$174.2941	$174.29	$174.30	$174.30
Purchase #4	$239.89	4.632%	$251.0017	$251.00	$251.00	$251.00
Purchase #5	$118.83	5.593%	$125.4762	$125.48	$125.50	$125.50
Purchase #6	$57.27	3.173%	$59.0872	$59.09	$59.10	$59.10
Purchase #7	$244.54	12.770%	$275.7678	$275.77	$275.75	$275.80
7 purchase totals =	$984.39		$1,066.3800	$1,066.39	$1,066.40	$1,066.40