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	$70.82	9.842%	$77.7901	$77.79	$77.80	$77.80
Purchase #2	$216.76	10.408%	$239.3204	$239.32	$239.30	$239.30
Purchase #3	$64.87	13.815%	$73.8318	$73.83	$73.85	$73.80
Purchase #4	$247.63	6.228%	$263.0524	$263.05	$263.05	$263.10
Purchase #5	$225.88	8.590%	$245.2831	$245.28	$245.30	$245.30
Purchase #6	$72.91	7.670%	$78.5022	$78.50	$78.50	$78.50
Purchase #7	$101.27	8.252%	$109.6268	$109.63	$109.65	$109.60
7 purchase totals =	$1,000.14		$1,087.4068	$1,087.40	$1,087.45	$1,087.40