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	$163.84	8.779%	$178.2235	$178.22	$178.20	$178.20
Purchase #2	$205.87	11.490%	$229.5245	$229.52	$229.50	$229.50
Purchase #3	$71.44	10.424%	$78.8869	$78.89	$78.90	$78.90
Purchase #4	$39.96	12.835%	$45.0889	$45.09	$45.10	$45.10
Purchase #5	$39.31	13.734%	$44.7088	$44.71	$44.70	$44.70
Purchase #6	$57.76	11.349%	$64.3152	$64.32	$64.30	$64.30
Purchase #7	$49.36	8.387%	$53.4998	$53.50	$53.50	$53.50
7 purchase totals =	$627.54		$694.2476	$694.25	$694.20	$694.20