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	$123.94	6.249%	$131.685	$131.69	$131.70	$131.70
Purchase #2	$58.57	12.544%	$65.917	$65.92	$65.90	$65.90
Purchase #3	$122.66	13.721%	$139.4902	$139.49	$139.50	$139.50
Purchase #4	$101.66	8.253%	$110.05	$110.05	$110.05	$110.10
Purchase #5	$152.98	12.129%	$171.5349	$171.53	$171.55	$171.50
Purchase #6	$90.25	11.106%	$100.2732	$100.27	$100.25	$100.30
Purchase #7	$123.49	8.205%	$133.6224	$133.62	$133.60	$133.60
7 purchase totals =	$773.55		$852.5727	$852.57	$852.55	$852.60