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	$101.35	3.722%	$105.1222	$105.12	$105.10	$105.10
Purchase #2	$194.49	9.175%	$212.3345	$212.33	$212.35	$212.30
Purchase #3	$199.70	6.409%	$212.4988	$212.50	$212.50	$212.50
Purchase #4	$35.64	13.513%	$40.456	$40.46	$40.45	$40.50
Purchase #5	$87.51	11.627%	$97.6848	$97.68	$97.70	$97.70
Purchase #6	$177.84	12.713%	$200.4488	$200.45	$200.45	$200.40
Purchase #7	$32.39	3.711%	$33.592	$33.59	$33.60	$33.60
7 purchase totals =	$828.92		$902.1371	$902.13	$902.15	$902.10