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	$53.79	7.396%	$57.7683	$57.77	$57.75	$57.80
Purchase #2	$100.49	13.392%	$113.9476	$113.95	$113.95	$113.90
Purchase #3	$63.99	12.321%	$71.8742	$71.87	$71.85	$71.90
Purchase #4	$221.70	7.718%	$238.8108	$238.81	$238.80	$238.80
Purchase #5	$100.38	11.106%	$111.5282	$111.53	$111.55	$111.50
Purchase #6	$28.76	11.452%	$32.0536	$32.05	$32.05	$32.10
Purchase #7	$75.63	7.629%	$81.3998	$81.40	$81.40	$81.40
7 purchase totals =	$644.74		$707.3825	$707.38	$707.35	$707.40