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	$88.78	13.198%	$100.4972	$100.50	$100.50	$100.50
Purchase #2	$135.66	3.272%	$140.0988	$140.10	$140.10	$140.10
Purchase #3	$77.29	13.544%	$87.7582	$87.76	$87.75	$87.80
Purchase #4	$229.97	11.720%	$256.9225	$256.92	$256.90	$256.90
Purchase #5	$38.81	9.412%	$42.4628	$42.46	$42.45	$42.50
Purchase #6	$93.61	12.615%	$105.4189	$105.42	$105.40	$105.40
Purchase #7	$5.82	11.687%	$6.5002	$6.50	$6.50	$6.50
7 purchase totals =	$669.94		$739.6586	$739.66	$739.60	$739.70