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	$44.36	13.367%	$50.2896	$50.29	$50.30	$50.30
Purchase #2	$71.31	9.833%	$78.3219	$78.32	$78.30	$78.30
Purchase #3	$102.32	7.155%	$109.641	$109.64	$109.65	$109.60
Purchase #4	$60.38	3.647%	$62.5821	$62.58	$62.60	$62.60
Purchase #5	$106.34	6.665%	$113.4276	$113.43	$113.45	$113.40
Purchase #6	$80.75	12.220%	$90.6177	$90.62	$90.60	$90.60
Purchase #7	$35.88	11.224%	$39.9072	$39.91	$39.90	$39.90
7 purchase totals =	$501.34		$544.7871	$544.79	$544.80	$544.70