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	$124.70	5.423%	$131.4625	$131.46	$131.45	$131.50
Purchase #2	$245.85	3.528%	$254.5236	$254.52	$254.50	$254.50
Purchase #3	$39.52	7.314%	$42.4105	$42.41	$42.40	$42.40
Purchase #4	$177.32	3.283%	$183.1414	$183.14	$183.15	$183.10
Purchase #5	$96.87	13.843%	$110.2797	$110.28	$110.30	$110.30
Purchase #6	$227.55	11.501%	$253.7205	$253.72	$253.70	$253.70
Purchase #7	$227.38	4.172%	$236.8663	$236.87	$236.85	$236.90
7 purchase totals =	$1,139.19		$1,212.4045	$1,212.40	$1,212.35	$1,212.40