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	$80.81	12.408%	$90.8369	$90.84	$90.85	$90.80
Purchase #2	$33.76	10.572%	$37.3291	$37.33	$37.35	$37.30
Purchase #3	$7.50	12.158%	$8.4119	$8.41	$8.40	$8.40
Purchase #4	$120.89	6.298%	$128.5037	$128.50	$128.50	$128.50
Purchase #5	$85.64	10.447%	$94.5868	$94.59	$94.60	$94.60
Purchase #6	$149.82	4.417%	$156.4375	$156.44	$156.45	$156.40
Purchase #7	$59.77	5.833%	$63.2564	$63.26	$63.25	$63.30
7 purchase totals =	$538.19		$579.3623	$579.37	$579.40	$579.30