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	$159.42	3.742%	$165.3855	$165.39	$165.40	$165.40
Purchase #2	$212.25	4.663%	$222.1472	$222.15	$222.15	$222.10
Purchase #3	$171.27	8.691%	$186.1551	$186.16	$186.15	$186.20
Purchase #4	$189.65	3.308%	$195.9236	$195.92	$195.90	$195.90
Purchase #5	$240.59	9.675%	$263.8671	$263.87	$263.85	$263.90
Purchase #6	$75.92	9.506%	$83.137	$83.14	$83.15	$83.10
Purchase #7	$35.56	7.104%	$38.0862	$38.09	$38.10	$38.10
7 purchase totals =	$1,084.66		$1,154.7017	$1,154.72	$1,154.70	$1,154.70