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	$210.39	9.477%	$230.3287	$230.33	$230.35	$230.30
Purchase #2	$153.99	11.140%	$171.1445	$171.14	$171.15	$171.10
Purchase #3	$153.51	4.542%	$160.4824	$160.48	$160.50	$160.50
Purchase #4	$146.56	9.268%	$160.1432	$160.14	$160.15	$160.10
Purchase #5	$129.89	3.807%	$134.8349	$134.83	$134.85	$134.80
Purchase #6	$169.69	12.307%	$190.5737	$190.57	$190.55	$190.60
Purchase #7	$180.74	8.658%	$196.3885	$196.39	$196.40	$196.40
7 purchase totals =	$1,144.77		$1,243.8959	$1,243.88	$1,243.95	$1,243.80