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	$216.49	10.784%	$239.8363	$239.84	$239.85	$239.80
Purchase #2	$67.28	4.266%	$70.1502	$70.15	$70.15	$70.20
Purchase #3	$39.92	13.705%	$45.391	$45.39	$45.40	$45.40
Purchase #4	$44.79	13.599%	$50.881	$50.88	$50.90	$50.90
Purchase #5	$42.57	10.441%	$47.0147	$47.01	$47.00	$47.00
Purchase #6	$67.69	12.831%	$76.3753	$76.38	$76.40	$76.40
Purchase #7	$58.62	4.346%	$61.1676	$61.17	$61.15	$61.20
7 purchase totals =	$537.36		$590.8161	$590.82	$590.85	$590.90