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	$49.99	11.833%	$55.9053	$55.91	$55.90	$55.90
Purchase #2	$69.80	12.128%	$78.2653	$78.27	$78.25	$78.30
Purchase #3	$42.34	6.676%	$45.1666	$45.17	$45.15	$45.20
Purchase #4	$102.31	13.705%	$116.3316	$116.33	$116.35	$116.30
Purchase #5	$243.32	13.749%	$276.7741	$276.77	$276.75	$276.80
Purchase #6	$112.54	3.485%	$116.462	$116.46	$116.45	$116.50
Purchase #7	$102.31	9.519%	$112.0489	$112.05	$112.05	$112.00
7 purchase totals =	$722.61		$800.9538	$800.96	$800.90	$801.00