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	$35.27	6.500%	$37.5626	$37.56	$37.55	$37.60
Purchase #2	$157.59	6.642%	$168.0571	$168.06	$168.05	$168.10
Purchase #3	$170.47	9.361%	$186.4277	$186.43	$186.45	$186.40
Purchase #4	$38.77	13.614%	$44.0481	$44.05	$44.05	$44.00
Purchase #5	$183.75	13.607%	$208.7529	$208.75	$208.75	$208.80
Purchase #6	$168.85	11.620%	$188.4704	$188.47	$188.45	$188.50
Purchase #7	$65.92	6.409%	$70.1448	$70.14	$70.15	$70.10
7 purchase totals =	$820.62		$903.4636	$903.46	$903.45	$903.50