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	$10.72	3.838%	$11.1314	$11.13	$11.15	$11.10
Purchase #2	$233.44	13.483%	$264.9147	$264.91	$264.90	$264.90
Purchase #3	$56.32	5.854%	$59.617	$59.62	$59.60	$59.60
Purchase #4	$137.84	8.470%	$149.515	$149.52	$149.50	$149.50
Purchase #5	$246.73	4.375%	$257.5244	$257.52	$257.50	$257.50
Purchase #6	$168.25	12.207%	$188.7883	$188.79	$188.80	$188.80
Purchase #7	$95.96	4.637%	$100.4097	$100.41	$100.40	$100.40
7 purchase totals =	$949.26		$1,031.9005	$1,031.90	$1,031.85	$1,031.80