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	$82.99	7.275%	$89.0275	$89.03	$89.05	$89.00
Purchase #2	$142.81	7.710%	$153.8207	$153.82	$153.80	$153.80
Purchase #3	$86.40	9.218%	$94.3644	$94.36	$94.35	$94.40
Purchase #4	$52.44	9.854%	$57.6074	$57.61	$57.60	$57.60
Purchase #5	$145.95	7.470%	$156.8525	$156.85	$156.85	$156.90
Purchase #6	$51.31	7.235%	$55.0223	$55.02	$55.00	$55.00
Purchase #7	$137.71	13.565%	$156.3904	$156.39	$156.40	$156.40
7 purchase totals =	$699.61		$763.0852	$763.08	$763.05	$763.10