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	$11.98	4.512%	$12.5205	$12.52	$12.50	$12.50
Purchase #2	$129.78	7.279%	$139.2267	$139.23	$139.25	$139.20
Purchase #3	$205.62	9.841%	$225.8551	$225.86	$225.85	$225.90
Purchase #4	$22.39	6.713%	$23.893	$23.89	$23.90	$23.90
Purchase #5	$41.79	10.555%	$46.2009	$46.20	$46.20	$46.20
Purchase #6	$198.41	6.502%	$211.3106	$211.31	$211.30	$211.30
Purchase #7	$142.94	13.693%	$162.5128	$162.51	$162.50	$162.50
7 purchase totals =	$752.91		$821.5196	$821.52	$821.50	$821.50