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	$171.76	7.663%	$184.922	$184.92	$184.90	$184.90
Purchase #2	$109.39	12.629%	$123.2049	$123.20	$123.20	$123.20
Purchase #3	$105.49	7.171%	$113.0547	$113.05	$113.05	$113.10
Purchase #4	$49.38	6.225%	$52.4539	$52.45	$52.45	$52.50
Purchase #5	$47.63	8.345%	$51.6047	$51.60	$51.60	$51.60
Purchase #6	$134.98	13.260%	$152.8783	$152.88	$152.90	$152.90
Purchase #7	$233.29	6.664%	$248.8364	$248.84	$248.85	$248.80
7 purchase totals =	$851.92		$926.9549	$926.94	$926.95	$927.00