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	$106.33	12.840%	$119.9828	$119.98	$120.00	$120.00
Purchase #2	$56.62	9.220%	$61.8404	$61.84	$61.85	$61.80
Purchase #3	$214.94	5.863%	$227.5419	$227.54	$227.55	$227.50
Purchase #4	$224.99	10.593%	$248.8232	$248.82	$248.80	$248.80
Purchase #5	$167.78	11.109%	$186.4187	$186.42	$186.40	$186.40
Purchase #6	$99.29	3.784%	$103.0471	$103.05	$103.05	$103.00
Purchase #7	$140.75	8.457%	$152.6532	$152.65	$152.65	$152.70
7 purchase totals =	$1,010.70		$1,100.3073	$1,100.30	$1,100.30	$1,100.20