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	$242.39	11.847%	$271.1059	$271.11	$271.10	$271.10
Purchase #2	$28.77	12.739%	$32.435	$32.44	$32.45	$32.40
Purchase #3	$187.81	5.809%	$198.7199	$198.72	$198.70	$198.70
Purchase #4	$58.72	10.484%	$64.8762	$64.88	$64.90	$64.90
Purchase #5	$89.26	7.302%	$95.7778	$95.78	$95.80	$95.80
Purchase #6	$116.76	9.742%	$128.1348	$128.13	$128.15	$128.10
Purchase #7	$17.48	5.873%	$18.5066	$18.51	$18.50	$18.50
7 purchase totals =	$741.19		$809.5562	$809.57	$809.60	$809.50