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	$151.74	13.558%	$172.3129	$172.31	$172.30	$172.30
Purchase #2	$176.41	11.517%	$196.7271	$196.73	$196.75	$196.70
Purchase #3	$100.97	9.807%	$110.8721	$110.87	$110.85	$110.90
Purchase #4	$34.39	3.121%	$35.4633	$35.46	$35.45	$35.50
Purchase #5	$38.90	4.254%	$40.5548	$40.55	$40.55	$40.60
Purchase #6	$155.51	13.736%	$176.8709	$176.87	$176.85	$176.90
Purchase #7	$53.67	6.680%	$57.2552	$57.26	$57.25	$57.30
7 purchase totals =	$711.59		$790.0563	$790.05	$790.00	$790.20