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	$88.30	5.176%	$92.8704	$92.87	$92.85	$92.90
Purchase #2	$62.34	13.656%	$70.8532	$70.85	$70.85	$70.90
Purchase #3	$12.44	9.120%	$13.5745	$13.57	$13.55	$13.60
Purchase #4	$206.72	10.403%	$228.2251	$228.23	$228.25	$228.20
Purchase #5	$124.72	11.559%	$139.1364	$139.14	$139.15	$139.10
Purchase #6	$96.33	4.731%	$100.8874	$100.89	$100.90	$100.90
Purchase #7	$126.68	10.571%	$140.0713	$140.07	$140.05	$140.10
7 purchase totals =	$717.53		$785.6183	$785.62	$785.60	$785.70