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	$84.96	6.521%	$90.5002	$90.50	$90.50	$90.50
Purchase #2	$147.44	5.466%	$155.4991	$155.50	$155.50	$155.50
Purchase #3	$194.62	9.206%	$212.5367	$212.54	$212.55	$212.50
Purchase #4	$39.75	10.557%	$43.9464	$43.95	$43.95	$43.90
Purchase #5	$141.30	5.268%	$148.7437	$148.74	$148.75	$148.70
Purchase #6	$229.85	8.107%	$248.4839	$248.48	$248.50	$248.50
Purchase #7	$143.64	13.307%	$162.7542	$162.75	$162.75	$162.80
7 purchase totals =	$981.56		$1,062.4642	$1,062.46	$1,062.50	$1,062.40