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	$81.78	11.697%	$91.3458	$91.35	$91.35	$91.30
Purchase #2	$210.42	8.500%	$228.3057	$228.31	$228.30	$228.30
Purchase #3	$43.53	7.452%	$46.7739	$46.77	$46.75	$46.80
Purchase #4	$116.30	12.454%	$130.784	$130.78	$130.80	$130.80
Purchase #5	$21.73	5.346%	$22.8917	$22.89	$22.90	$22.90
Purchase #6	$94.77	6.453%	$100.8855	$100.89	$100.90	$100.90
Purchase #7	$160.82	9.702%	$176.4228	$176.42	$176.40	$176.40
7 purchase totals =	$729.35		$797.4094	$797.41	$797.40	$797.40