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	$80.54	6.543%	$85.8097	$85.81	$85.80	$85.80
Purchase #2	$151.49	10.422%	$167.2783	$167.28	$167.30	$167.30
Purchase #3	$151.54	10.222%	$167.0304	$167.03	$167.05	$167.00
Purchase #4	$28.34	11.259%	$31.5308	$31.53	$31.55	$31.50
Purchase #5	$131.27	8.486%	$142.4096	$142.41	$142.40	$142.40
Purchase #6	$44.38	11.820%	$49.6257	$49.63	$49.65	$49.60
Purchase #7	$82.33	5.580%	$86.924	$86.92	$86.90	$86.90
7 purchase totals =	$669.89		$730.6085	$730.61	$730.65	$730.50