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	$249.39	6.336%	$265.1914	$265.19	$265.20	$265.20
Purchase #2	$211.27	11.241%	$235.0189	$235.02	$235.00	$235.00
Purchase #3	$161.76	6.870%	$172.8729	$172.87	$172.85	$172.90
Purchase #4	$18.34	10.138%	$20.1993	$20.20	$20.20	$20.20
Purchase #5	$105.93	9.616%	$116.1162	$116.12	$116.10	$116.10
Purchase #6	$135.74	6.734%	$144.8807	$144.88	$144.90	$144.90
Purchase #7	$154.77	7.172%	$165.8701	$165.87	$165.85	$165.90
7 purchase totals =	$1,037.20		$1,120.1495	$1,120.15	$1,120.10	$1,120.20