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	$168.66	12.241%	$189.3057	$189.31	$189.30	$189.30
Purchase #2	$232.40	11.470%	$259.0563	$259.06	$259.05	$259.10
Purchase #3	$9.39	12.598%	$10.573	$10.57	$10.55	$10.60
Purchase #4	$210.54	12.607%	$237.0828	$237.08	$237.10	$237.10
Purchase #5	$239.77	6.143%	$254.4991	$254.50	$254.50	$254.50
Purchase #6	$110.83	11.810%	$123.919	$123.92	$123.90	$123.90
Purchase #7	$128.73	11.178%	$143.1194	$143.12	$143.10	$143.10
7 purchase totals =	$1,100.32		$1,217.5553	$1,217.56	$1,217.50	$1,217.60