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	$86.59	3.805%	$89.8847	$89.88	$89.90	$89.90
Purchase #2	$188.83	11.123%	$209.8336	$209.83	$209.85	$209.80
Purchase #3	$64.47	3.399%	$66.6613	$66.66	$66.65	$66.70
Purchase #4	$96.73	12.378%	$108.7032	$108.70	$108.70	$108.70
Purchase #5	$234.32	8.460%	$254.1435	$254.14	$254.15	$254.10
Purchase #6	$156.56	12.218%	$175.6885	$175.69	$175.70	$175.70
Purchase #7	$187.64	11.767%	$209.7196	$209.72	$209.70	$209.70
7 purchase totals =	$1,015.14		$1,114.6344	$1,114.62	$1,114.65	$1,114.60