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	$52.30	10.216%	$57.643	$57.64	$57.65	$57.60
Purchase #2	$82.60	3.420%	$85.4249	$85.42	$85.40	$85.40
Purchase #3	$120.32	13.834%	$136.9651	$136.97	$136.95	$137.00
Purchase #4	$199.54	6.201%	$211.9135	$211.91	$211.90	$211.90
Purchase #5	$216.33	7.854%	$233.3206	$233.32	$233.30	$233.30
Purchase #6	$216.68	4.150%	$225.6722	$225.67	$225.65	$225.70
Purchase #7	$105.56	9.667%	$115.7645	$115.76	$115.75	$115.80
7 purchase totals =	$993.33		$1,066.7038	$1,066.69	$1,066.60	$1,066.70