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	$48.53	13.463%	$55.0636	$55.06	$55.05	$55.10
Purchase #2	$46.71	13.634%	$53.0784	$53.08	$53.10	$53.10
Purchase #3	$196.90	6.299%	$209.3027	$209.30	$209.30	$209.30
Purchase #4	$151.71	8.305%	$164.3095	$164.31	$164.30	$164.30
Purchase #5	$102.75	8.409%	$111.3902	$111.39	$111.40	$111.40
Purchase #6	$128.48	13.447%	$145.7567	$145.76	$145.75	$145.80
Purchase #7	$180.32	10.676%	$199.571	$199.57	$199.55	$199.60
7 purchase totals =	$855.40		$938.4721	$938.47	$938.45	$938.60