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	$234.98	3.257%	$242.6333	$242.63	$242.65	$242.60
Purchase #2	$231.41	10.541%	$255.8029	$255.80	$255.80	$255.80
Purchase #3	$121.58	5.658%	$128.459	$128.46	$128.45	$128.50
Purchase #4	$42.66	5.281%	$44.9129	$44.91	$44.90	$44.90
Purchase #5	$91.31	8.306%	$98.8942	$98.89	$98.90	$98.90
Purchase #6	$72.43	8.151%	$78.3338	$78.33	$78.35	$78.30
Purchase #7	$58.78	6.710%	$62.7241	$62.72	$62.70	$62.70
7 purchase totals =	$853.15		$911.7602	$911.74	$911.75	$911.70