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	$212.32	4.662%	$222.2184	$222.22	$222.20	$222.20
Purchase #2	$86.29	7.330%	$92.6151	$92.62	$92.60	$92.60
Purchase #3	$186.51	12.195%	$209.2549	$209.25	$209.25	$209.30
Purchase #4	$25.78	10.230%	$28.4173	$28.42	$28.40	$28.40
Purchase #5	$184.98	13.428%	$209.8191	$209.82	$209.80	$209.80
Purchase #6	$25.32	8.294%	$27.42	$27.42	$27.40	$27.40
Purchase #7	$40.59	3.819%	$42.1401	$42.14	$42.15	$42.10
7 purchase totals =	$761.79		$831.8849	$831.89	$831.80	$831.80