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	$111.79	7.786%	$120.494	$120.49	$120.50	$120.50
Purchase #2	$198.83	6.350%	$211.4557	$211.46	$211.45	$211.50
Purchase #3	$48.26	11.756%	$53.9334	$53.93	$53.95	$53.90
Purchase #4	$200.60	4.452%	$209.5307	$209.53	$209.55	$209.50
Purchase #5	$101.40	8.320%	$109.8365	$109.84	$109.85	$109.80
Purchase #6	$52.98	11.172%	$58.8989	$58.90	$58.90	$58.90
Purchase #7	$81.96	10.649%	$90.6879	$90.69	$90.70	$90.70
7 purchase totals =	$795.82		$854.8371	$854.84	$854.90	$854.80