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	$30.59	5.590%	$32.3	$32.30	$32.30	$32.30
Purchase #2	$239.83	12.280%	$269.2811	$269.28	$269.30	$269.30
Purchase #3	$40.59	12.179%	$45.5335	$45.53	$45.55	$45.50
Purchase #4	$236.83	5.703%	$250.3364	$250.34	$250.35	$250.30
Purchase #5	$49.96	5.272%	$52.5939	$52.59	$52.60	$52.60
Purchase #6	$151.26	13.241%	$171.2883	$171.29	$171.30	$171.30
Purchase #7	$71.27	10.338%	$78.6379	$78.64	$78.65	$78.60
7 purchase totals =	$820.33		$899.9711	$899.97	$900.05	$899.90