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	$137.72	5.853%	$145.7808	$145.78	$145.80	$145.80
Purchase #2	$93.44	13.755%	$106.2927	$106.29	$106.30	$106.30
Purchase #3	$92.73	13.706%	$105.4396	$105.44	$105.45	$105.40
Purchase #4	$155.82	10.430%	$172.072	$172.07	$172.05	$172.10
Purchase #5	$159.96	7.474%	$171.9154	$171.92	$171.90	$171.90
Purchase #6	$115.72	5.842%	$122.4804	$122.48	$122.50	$122.50
Purchase #7	$217.59	4.382%	$227.1248	$227.12	$227.10	$227.10
7 purchase totals =	$972.98		$1,051.1057	$1,051.10	$1,051.10	$1,051.10