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	$61.78	13.744%	$70.271	$70.27	$70.25	$70.30
Purchase #2	$95.79	9.188%	$104.5912	$104.59	$104.60	$104.60
Purchase #3	$213.36	4.261%	$222.4513	$222.45	$222.45	$222.50
Purchase #4	$98.62	5.588%	$104.1309	$104.13	$104.15	$104.10
Purchase #5	$224.78	10.109%	$247.503	$247.50	$247.50	$247.50
Purchase #6	$39.59	10.664%	$43.8119	$43.81	$43.80	$43.80
Purchase #7	$92.71	3.798%	$96.2311	$96.23	$96.25	$96.20
7 purchase totals =	$826.63		$888.9904	$888.98	$889.00	$889.00