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	$184.32	7.805%	$198.7062	$198.71	$198.70	$198.70
Purchase #2	$246.96	11.467%	$275.2789	$275.28	$275.30	$275.30
Purchase #3	$92.67	8.317%	$100.3774	$100.38	$100.40	$100.40
Purchase #4	$83.84	11.845%	$93.7708	$93.77	$93.75	$93.80
Purchase #5	$114.27	3.315%	$118.0581	$118.06	$118.05	$118.10
Purchase #6	$81.98	4.166%	$85.3953	$85.40	$85.40	$85.40
Purchase #7	$69.36	13.739%	$78.8894	$78.89	$78.90	$78.90
7 purchase totals =	$873.40		$950.4761	$950.49	$950.50	$950.60