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	$165.70	10.740%	$183.4962	$183.50	$183.50	$183.50
Purchase #2	$80.26	11.106%	$89.1737	$89.17	$89.15	$89.20
Purchase #3	$94.28	6.820%	$100.7099	$100.71	$100.70	$100.70
Purchase #4	$127.92	12.368%	$143.7411	$143.74	$143.75	$143.70
Purchase #5	$117.71	5.390%	$124.0546	$124.05	$124.05	$124.10
Purchase #6	$175.71	8.867%	$191.2902	$191.29	$191.30	$191.30
Purchase #7	$77.79	10.102%	$85.6483	$85.65	$85.65	$85.60
7 purchase totals =	$839.37		$918.1140	$918.11	$918.10	$918.10