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	$20.31	5.109%	$21.3476	$21.35	$21.35	$21.30
Purchase #2	$75.59	3.780%	$78.4473	$78.45	$78.45	$78.40
Purchase #3	$107.78	5.415%	$113.6163	$113.62	$113.60	$113.60
Purchase #4	$106.50	6.432%	$113.3501	$113.35	$113.35	$113.40
Purchase #5	$48.53	11.238%	$53.9838	$53.98	$54.00	$54.00
Purchase #6	$44.71	13.776%	$50.8692	$50.87	$50.85	$50.90
Purchase #7	$107.88	10.436%	$119.1384	$119.14	$119.15	$119.10
7 purchase totals =	$511.30		$550.7527	$550.76	$550.75	$550.70