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	$167.90	6.813%	$179.339	$179.34	$179.35	$179.30
Purchase #2	$210.94	7.625%	$227.0242	$227.02	$227.00	$227.00
Purchase #3	$29.70	9.870%	$32.6314	$32.63	$32.65	$32.60
Purchase #4	$158.79	3.607%	$164.5176	$164.52	$164.50	$164.50
Purchase #5	$83.52	13.522%	$94.8136	$94.81	$94.80	$94.80
Purchase #6	$26.57	4.399%	$27.7388	$27.74	$27.75	$27.70
Purchase #7	$82.61	8.543%	$89.6674	$89.67	$89.65	$89.70
7 purchase totals =	$760.03		$815.7320	$815.73	$815.70	$815.60