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	$116.97	12.799%	$131.941	$131.94	$131.95	$131.90
Purchase #2	$117.62	11.355%	$130.9758	$130.98	$131.00	$131.00
Purchase #3	$79.47	7.339%	$85.3023	$85.30	$85.30	$85.30
Purchase #4	$100.66	10.336%	$111.0642	$111.06	$111.05	$111.10
Purchase #5	$99.70	4.712%	$104.3979	$104.40	$104.40	$104.40
Purchase #6	$163.44	10.720%	$180.9608	$180.96	$180.95	$181.00
Purchase #7	$137.54	7.692%	$148.1196	$148.12	$148.10	$148.10
7 purchase totals =	$815.40		$892.7616	$892.76	$892.75	$892.80