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	$137.59	8.528%	$149.3237	$149.32	$149.30	$149.30
Purchase #2	$42.55	11.181%	$47.3075	$47.31	$47.30	$47.30
Purchase #3	$118.97	5.459%	$125.4646	$125.46	$125.45	$125.50
Purchase #4	$231.69	3.783%	$240.4548	$240.45	$240.45	$240.50
Purchase #5	$91.87	9.621%	$100.7088	$100.71	$100.70	$100.70
Purchase #6	$76.57	8.476%	$83.0601	$83.06	$83.05	$83.10
Purchase #7	$244.94	12.384%	$275.2734	$275.27	$275.25	$275.30
7 purchase totals =	$944.18		$1,021.5929	$1,021.58	$1,021.50	$1,021.70