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	$94.48	3.173%	$97.4779	$97.48	$97.50	$97.50
Purchase #2	$162.38	10.642%	$179.6605	$179.66	$179.65	$179.70
Purchase #3	$96.48	13.559%	$109.5617	$109.56	$109.55	$109.60
Purchase #4	$42.70	7.354%	$45.8402	$45.84	$45.85	$45.80
Purchase #5	$211.34	8.160%	$228.5853	$228.59	$228.60	$228.60
Purchase #6	$74.74	7.800%	$80.5697	$80.57	$80.55	$80.60
Purchase #7	$81.64	10.414%	$90.142	$90.14	$90.15	$90.10
7 purchase totals =	$763.76		$831.8373	$831.84	$831.85	$831.90