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	$7.56	9.458%	$8.275	$8.28	$8.30	$8.30
Purchase #2	$159.38	4.472%	$166.5075	$166.51	$166.50	$166.50
Purchase #3	$85.80	10.572%	$94.8708	$94.87	$94.85	$94.90
Purchase #4	$226.63	6.717%	$241.8527	$241.85	$241.85	$241.90
Purchase #5	$35.78	12.756%	$40.3441	$40.34	$40.35	$40.30
Purchase #6	$179.38	4.398%	$187.2691	$187.27	$187.25	$187.30
Purchase #7	$32.33	5.533%	$34.1188	$34.12	$34.10	$34.10
7 purchase totals =	$726.86		$773.2380	$773.24	$773.20	$773.30