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	$29.61	6.389%	$31.5018	$31.50	$31.50	$31.50
Purchase #2	$33.76	4.355%	$35.2302	$35.23	$35.25	$35.20
Purchase #3	$51.94	3.459%	$53.7366	$53.74	$53.75	$53.70
Purchase #4	$174.55	8.445%	$189.2907	$189.29	$189.30	$189.30
Purchase #5	$71.93	13.754%	$81.8233	$81.82	$81.80	$81.80
Purchase #6	$159.29	7.215%	$170.7828	$170.78	$170.80	$170.80
Purchase #7	$141.62	10.758%	$156.8555	$156.86	$156.85	$156.90
7 purchase totals =	$662.70		$719.2209	$719.22	$719.25	$719.20