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	$238.34	6.281%	$253.3101	$253.31	$253.30	$253.30
Purchase #2	$176.78	7.174%	$189.4622	$189.46	$189.45	$189.50
Purchase #3	$59.75	4.759%	$62.5935	$62.59	$62.60	$62.60
Purchase #4	$213.39	11.663%	$238.2777	$238.28	$238.30	$238.30
Purchase #5	$148.42	4.480%	$155.0692	$155.07	$155.05	$155.10
Purchase #6	$174.66	12.166%	$195.9091	$195.91	$195.90	$195.90
Purchase #7	$164.86	8.241%	$178.4461	$178.45	$178.45	$178.40
7 purchase totals =	$1,176.20		$1,273.0679	$1,273.07	$1,273.05	$1,273.10