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	$160.93	10.691%	$178.135	$178.14	$178.15	$178.10
Purchase #2	$168.55	5.552%	$177.9079	$177.91	$177.90	$177.90
Purchase #3	$98.51	11.551%	$109.8889	$109.89	$109.90	$109.90
Purchase #4	$134.79	13.327%	$152.7535	$152.75	$152.75	$152.80
Purchase #5	$35.95	4.297%	$37.4948	$37.49	$37.50	$37.50
Purchase #6	$156.69	7.464%	$168.3853	$168.39	$168.40	$168.40
Purchase #7	$63.39	4.517%	$66.2533	$66.25	$66.25	$66.30
7 purchase totals =	$818.81		$890.8187	$890.82	$890.85	$890.90