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	$160.71	6.541%	$171.222	$171.22	$171.20	$171.20
Purchase #2	$183.25	4.182%	$190.9135	$190.91	$190.90	$190.90
Purchase #3	$229.78	5.683%	$242.8384	$242.84	$242.85	$242.80
Purchase #4	$61.49	10.440%	$67.9096	$67.91	$67.90	$67.90
Purchase #5	$112.50	4.569%	$117.6401	$117.64	$117.65	$117.60
Purchase #6	$81.95	10.458%	$90.5203	$90.52	$90.50	$90.50
Purchase #7	$85.83	9.111%	$93.65	$93.65	$93.65	$93.70
7 purchase totals =	$915.51		$974.6939	$974.69	$974.65	$974.60