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	$57.36	3.427%	$59.3257	$59.33	$59.35	$59.30
Purchase #2	$144.58	9.781%	$158.7214	$158.72	$158.70	$158.70
Purchase #3	$99.70	12.401%	$112.0638	$112.06	$112.05	$112.10
Purchase #4	$110.91	11.596%	$123.7711	$123.77	$123.75	$123.80
Purchase #5	$130.27	3.728%	$135.1265	$135.13	$135.15	$135.10
Purchase #6	$37.96	12.431%	$42.6788	$42.68	$42.70	$42.70
Purchase #7	$174.60	4.665%	$182.7451	$182.75	$182.75	$182.70
7 purchase totals =	$755.38		$814.4324	$814.44	$814.45	$814.40