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	$155.69	10.867%	$172.6088	$172.61	$172.60	$172.60
Purchase #2	$98.71	11.256%	$109.8208	$109.82	$109.80	$109.80
Purchase #3	$155.33	13.592%	$176.4425	$176.44	$176.45	$176.40
Purchase #4	$100.27	5.518%	$105.8029	$105.80	$105.80	$105.80
Purchase #5	$60.82	4.499%	$63.5563	$63.56	$63.55	$63.60
Purchase #6	$105.78	13.581%	$120.146	$120.15	$120.15	$120.10
Purchase #7	$240.67	4.283%	$250.9779	$250.98	$251.00	$251.00
7 purchase totals =	$917.27		$999.3552	$999.36	$999.35	$999.30