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	$64.27	5.652%	$67.9025	$67.90	$67.90	$67.90
Purchase #2	$115.72	11.104%	$128.5695	$128.57	$128.55	$128.60
Purchase #3	$138.80	10.346%	$153.1602	$153.16	$153.15	$153.20
Purchase #4	$78.30	8.449%	$84.9156	$84.92	$84.90	$84.90
Purchase #5	$130.84	6.666%	$139.5618	$139.56	$139.55	$139.60
Purchase #6	$148.96	7.862%	$160.6712	$160.67	$160.65	$160.70
Purchase #7	$173.83	10.356%	$191.8318	$191.83	$191.85	$191.80
7 purchase totals =	$850.72		$926.6126	$926.61	$926.55	$926.70