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	$172.85	6.115%	$183.4198	$183.42	$183.40	$183.40
Purchase #2	$236.53	5.845%	$250.3552	$250.36	$250.35	$250.40
Purchase #3	$118.76	4.148%	$123.6862	$123.69	$123.70	$123.70
Purchase #4	$131.34	6.805%	$140.2777	$140.28	$140.30	$140.30
Purchase #5	$103.78	5.692%	$109.6872	$109.69	$109.70	$109.70
Purchase #6	$238.59	7.479%	$256.4341	$256.43	$256.45	$256.40
Purchase #7	$179.73	4.685%	$188.1504	$188.15	$188.15	$188.20
7 purchase totals =	$1,181.58		$1,252.0106	$1,252.02	$1,252.05	$1,252.10