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	$241.96	12.121%	$271.288	$271.29	$271.30	$271.30
Purchase #2	$54.62	13.394%	$61.9358	$61.94	$61.95	$61.90
Purchase #3	$199.73	5.378%	$210.4715	$210.47	$210.45	$210.50
Purchase #4	$123.89	10.582%	$137	$137.00	$137.00	$137.00
Purchase #5	$101.55	11.197%	$112.9206	$112.92	$112.90	$112.90
Purchase #6	$128.50	11.794%	$143.6553	$143.66	$143.65	$143.70
Purchase #7	$85.35	13.227%	$96.6392	$96.64	$96.65	$96.60
7 purchase totals =	$935.60		$1,033.9104	$1,033.92	$1,033.90	$1,033.90