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	$201.98	10.299%	$222.7819	$222.78	$222.80	$222.80
Purchase #2	$83.33	7.833%	$89.8572	$89.86	$89.85	$89.90
Purchase #3	$137.55	3.233%	$141.997	$142.00	$142.00	$142.00
Purchase #4	$159.59	3.839%	$165.7167	$165.72	$165.70	$165.70
Purchase #5	$66.92	10.648%	$74.0456	$74.05	$74.05	$74.00
Purchase #6	$211.47	9.146%	$230.811	$230.81	$230.80	$230.80
Purchase #7	$35.81	12.776%	$40.3851	$40.39	$40.40	$40.40
7 purchase totals =	$896.65		$965.5945	$965.61	$965.60	$965.60