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	$219.55	6.829%	$234.5431	$234.54	$234.55	$234.50
Purchase #2	$170.59	7.124%	$182.7428	$182.74	$182.75	$182.70
Purchase #3	$186.53	13.111%	$210.9859	$210.99	$211.00	$211.00
Purchase #4	$104.42	11.506%	$116.4346	$116.43	$116.45	$116.40
Purchase #5	$125.72	10.591%	$139.035	$139.04	$139.05	$139.00
Purchase #6	$109.63	4.406%	$114.4603	$114.46	$114.45	$114.50
Purchase #7	$127.91	10.289%	$141.0707	$141.07	$141.05	$141.10
7 purchase totals =	$1,044.35		$1,139.2724	$1,139.27	$1,139.30	$1,139.20