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	$37.32	6.747%	$39.838	$39.84	$39.85	$39.80
Purchase #2	$180.46	7.623%	$194.2165	$194.22	$194.20	$194.20
Purchase #3	$89.51	5.289%	$94.2442	$94.24	$94.25	$94.20
Purchase #4	$20.48	4.400%	$21.3811	$21.38	$21.40	$21.40
Purchase #5	$68.81	13.523%	$78.1152	$78.12	$78.10	$78.10
Purchase #6	$32.95	12.653%	$37.1192	$37.12	$37.10	$37.10
Purchase #7	$77.95	7.740%	$83.9833	$83.98	$84.00	$84.00
7 purchase totals =	$507.48		$548.8975	$548.90	$548.90	$548.80