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	$38.25	13.155%	$43.2818	$43.28	$43.30	$43.30
Purchase #2	$117.71	9.399%	$128.7736	$128.77	$128.75	$128.80
Purchase #3	$173.30	8.758%	$188.4776	$188.48	$188.50	$188.50
Purchase #4	$157.58	13.184%	$178.3553	$178.36	$178.35	$178.40
Purchase #5	$94.59	5.584%	$99.8719	$99.87	$99.85	$99.90
Purchase #6	$76.76	4.753%	$80.4084	$80.41	$80.40	$80.40
Purchase #7	$105.70	13.548%	$120.0202	$120.02	$120.00	$120.00
7 purchase totals =	$763.89		$839.1888	$839.19	$839.15	$839.30