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	$39.68	11.750%	$44.3424	$44.34	$44.35	$44.30
Purchase #2	$112.51	13.823%	$128.0623	$128.06	$128.05	$128.10
Purchase #3	$233.33	7.169%	$250.0574	$250.06	$250.05	$250.10
Purchase #4	$106.73	11.222%	$118.7072	$118.71	$118.70	$118.70
Purchase #5	$207.82	12.119%	$233.0057	$233.01	$233.00	$233.00
Purchase #6	$243.61	12.354%	$273.7056	$273.71	$273.70	$273.70
Purchase #7	$133.77	13.718%	$152.1206	$152.12	$152.10	$152.10
7 purchase totals =	$1,077.45		$1,200.0012	$1,200.01	$1,199.95	$1,200.00