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	$90.89	3.763%	$94.3102	$94.31	$94.30	$94.30
Purchase #2	$133.71	4.622%	$139.8901	$139.89	$139.90	$139.90
Purchase #3	$193.80	13.187%	$219.3564	$219.36	$219.35	$219.40
Purchase #4	$193.78	12.765%	$218.516	$218.52	$218.50	$218.50
Purchase #5	$54.39	5.389%	$57.3211	$57.32	$57.30	$57.30
Purchase #6	$35.90	9.216%	$39.2085	$39.21	$39.20	$39.20
Purchase #7	$196.84	13.279%	$222.9784	$222.98	$223.00	$223.00
7 purchase totals =	$899.31		$991.5807	$991.59	$991.55	$991.60