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	$49.29	7.563%	$53.0178	$53.02	$53.00	$53.00
Purchase #2	$53.91	4.158%	$56.1516	$56.15	$56.15	$56.20
Purchase #3	$102.31	10.704%	$113.2613	$113.26	$113.25	$113.30
Purchase #4	$203.43	6.381%	$216.4109	$216.41	$216.40	$216.40
Purchase #5	$36.83	9.323%	$40.2637	$40.26	$40.25	$40.30
Purchase #6	$72.38	11.526%	$80.7225	$80.72	$80.70	$80.70
Purchase #7	$32.63	10.194%	$35.9563	$35.96	$35.95	$36.00
7 purchase totals =	$550.78		$595.7841	$595.78	$595.70	$595.90