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	$80.45	12.103%	$90.1869	$90.19	$90.20	$90.20
Purchase #2	$67.52	3.271%	$69.7286	$69.73	$69.75	$69.70
Purchase #3	$164.66	10.548%	$182.0283	$182.03	$182.05	$182.00
Purchase #4	$69.33	3.309%	$71.6241	$71.62	$71.60	$71.60
Purchase #5	$93.46	13.304%	$105.8939	$105.89	$105.90	$105.90
Purchase #6	$156.68	5.563%	$165.3961	$165.40	$165.40	$165.40
Purchase #7	$225.34	13.659%	$256.1192	$256.12	$256.10	$256.10
7 purchase totals =	$857.44		$940.9771	$940.98	$941.00	$940.90