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	$115.61	6.646%	$123.2934	$123.29	$123.30	$123.30
Purchase #2	$244.72	6.154%	$259.7801	$259.78	$259.80	$259.80
Purchase #3	$129.55	11.115%	$143.9495	$143.95	$143.95	$143.90
Purchase #4	$136.40	4.413%	$142.4193	$142.42	$142.40	$142.40
Purchase #5	$160.84	5.439%	$169.5881	$169.59	$169.60	$169.60
Purchase #6	$96.29	4.820%	$100.9312	$100.93	$100.95	$100.90
Purchase #7	$222.64	11.486%	$248.2124	$248.21	$248.20	$248.20
7 purchase totals =	$1,106.05		$1,188.1740	$1,188.17	$1,188.20	$1,188.10