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	$92.74	8.168%	$100.315	$100.32	$100.30	$100.30
Purchase #2	$199.60	6.442%	$212.4582	$212.46	$212.45	$212.50
Purchase #3	$77.57	6.754%	$82.8091	$82.81	$82.80	$82.80
Purchase #4	$138.35	8.594%	$150.2398	$150.24	$150.25	$150.20
Purchase #5	$74.25	10.599%	$82.1198	$82.12	$82.10	$82.10
Purchase #6	$84.86	6.773%	$90.6076	$90.61	$90.60	$90.60
Purchase #7	$123.66	9.617%	$135.5524	$135.55	$135.55	$135.60
7 purchase totals =	$791.03		$854.1019	$854.11	$854.05	$854.10