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	$39.29	7.152%	$42.1	$42.10	$42.10	$42.10
Purchase #2	$222.31	4.564%	$232.4562	$232.46	$232.45	$232.50
Purchase #3	$46.83	12.328%	$52.6032	$52.60	$52.60	$52.60
Purchase #4	$156.53	3.323%	$161.7315	$161.73	$161.75	$161.70
Purchase #5	$124.69	10.458%	$137.7301	$137.73	$137.75	$137.70
Purchase #6	$164.96	3.301%	$170.4053	$170.41	$170.40	$170.40
Purchase #7	$28.69	12.523%	$32.2828	$32.28	$32.30	$32.30
7 purchase totals =	$783.30		$829.3091	$829.31	$829.35	$829.30