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	$111.85	11.286%	$124.4734	$124.47	$124.45	$124.50
Purchase #2	$81.88	4.524%	$85.5843	$85.58	$85.60	$85.60
Purchase #3	$66.32	7.672%	$71.4081	$71.41	$71.40	$71.40
Purchase #4	$76.90	8.549%	$83.4742	$83.47	$83.45	$83.50
Purchase #5	$208.76	6.399%	$222.1186	$222.12	$222.10	$222.10
Purchase #6	$55.97	13.530%	$63.5427	$63.54	$63.55	$63.50
Purchase #7	$224.50	13.374%	$254.5246	$254.52	$254.50	$254.50
7 purchase totals =	$826.18		$905.1259	$905.11	$905.05	$905.10