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	$218.64	6.530%	$232.9172	$232.92	$232.90	$232.90
Purchase #2	$168.46	12.266%	$189.1233	$189.12	$189.10	$189.10
Purchase #3	$247.51	12.834%	$279.2754	$279.28	$279.30	$279.30
Purchase #4	$51.69	3.292%	$53.3916	$53.39	$53.40	$53.40
Purchase #5	$146.95	12.206%	$164.8867	$164.89	$164.90	$164.90
Purchase #6	$160.95	5.874%	$170.4042	$170.40	$170.40	$170.40
Purchase #7	$127.56	12.352%	$143.3162	$143.32	$143.30	$143.30
7 purchase totals =	$1,121.76		$1,233.3146	$1,233.32	$1,233.30	$1,233.30