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	$55.97	3.269%	$57.7997	$57.80	$57.80	$57.80
Purchase #2	$107.65	12.292%	$120.8823	$120.88	$120.90	$120.90
Purchase #3	$88.59	6.843%	$94.6522	$94.65	$94.65	$94.70
Purchase #4	$28.77	4.426%	$30.0434	$30.04	$30.05	$30.00
Purchase #5	$42.50	7.267%	$45.5885	$45.59	$45.60	$45.60
Purchase #6	$129.40	10.426%	$142.8912	$142.89	$142.90	$142.90
Purchase #7	$55.40	7.545%	$59.5799	$59.58	$59.60	$59.60
7 purchase totals =	$508.28		$551.4372	$551.43	$551.50	$551.50