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	$30.66	5.755%	$32.4245	$32.42	$32.40	$32.40
Purchase #2	$173.61	5.311%	$182.8304	$182.83	$182.85	$182.80
Purchase #3	$89.52	13.630%	$101.7216	$101.72	$101.70	$101.70
Purchase #4	$103.76	13.362%	$117.6244	$117.62	$117.60	$117.60
Purchase #5	$95.30	5.212%	$100.267	$100.27	$100.25	$100.30
Purchase #6	$225.53	10.690%	$249.6392	$249.64	$249.65	$249.60
Purchase #7	$199.31	9.533%	$218.3102	$218.31	$218.30	$218.30
7 purchase totals =	$917.69		$1,002.8173	$1,002.81	$1,002.75	$1,002.70