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	$41.35	9.843%	$45.4201	$45.42	$45.40	$45.40
Purchase #2	$48.87	4.694%	$51.164	$51.16	$51.15	$51.20
Purchase #3	$136.66	8.738%	$148.6014	$148.60	$148.60	$148.60
Purchase #4	$90.82	8.644%	$98.6705	$98.67	$98.65	$98.70
Purchase #5	$128.74	10.561%	$142.3362	$142.34	$142.35	$142.30
Purchase #6	$194.49	9.337%	$212.6495	$212.65	$212.65	$212.60
Purchase #7	$40.72	12.677%	$45.8821	$45.88	$45.90	$45.90
7 purchase totals =	$681.65		$744.7238	$744.72	$744.70	$744.70