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	$151.72	13.565%	$172.3008	$172.30	$172.30	$172.30
Purchase #2	$30.99	12.607%	$34.8969	$34.90	$34.90	$34.90
Purchase #3	$168.72	12.571%	$189.9298	$189.93	$189.95	$189.90
Purchase #4	$73.46	6.287%	$78.0784	$78.08	$78.10	$78.10
Purchase #5	$13.46	6.528%	$14.3387	$14.34	$14.35	$14.30
Purchase #6	$177.54	4.639%	$185.7761	$185.78	$185.80	$185.80
Purchase #7	$53.33	3.133%	$55.0008	$55.00	$55.00	$55.00
7 purchase totals =	$669.22		$730.3215	$730.33	$730.40	$730.30