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	$240.40	10.785%	$266.3271	$266.33	$266.35	$266.30
Purchase #2	$247.85	10.321%	$273.4306	$273.43	$273.45	$273.40
Purchase #3	$149.70	6.258%	$159.0682	$159.07	$159.05	$159.10
Purchase #4	$84.67	4.502%	$88.4818	$88.48	$88.50	$88.50
Purchase #5	$49.30	12.513%	$55.4689	$55.47	$55.45	$55.50
Purchase #6	$207.32	5.555%	$218.8366	$218.84	$218.85	$218.80
Purchase #7	$78.52	13.736%	$89.3055	$89.31	$89.30	$89.30
7 purchase totals =	$1,057.76		$1,150.9187	$1,150.93	$1,150.95	$1,150.90