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	$52.81	11.460%	$58.862	$58.86	$58.85	$58.90
Purchase #2	$56.47	7.617%	$60.7713	$60.77	$60.75	$60.80
Purchase #3	$72.76	7.190%	$77.9914	$77.99	$78.00	$78.00
Purchase #4	$174.78	4.545%	$182.7238	$182.72	$182.70	$182.70
Purchase #5	$37.53	12.315%	$42.1518	$42.15	$42.15	$42.20
Purchase #6	$77.55	7.168%	$83.1088	$83.11	$83.10	$83.10
Purchase #7	$46.94	13.124%	$53.1004	$53.10	$53.10	$53.10
7 purchase totals =	$518.84		$558.7095	$558.70	$558.65	$558.80