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	$94.34	11.724%	$105.4004	$105.40	$105.40	$105.40
Purchase #2	$80.61	7.343%	$86.5292	$86.53	$86.55	$86.50
Purchase #3	$205.54	3.282%	$212.2858	$212.29	$212.30	$212.30
Purchase #4	$58.73	9.740%	$64.4503	$64.45	$64.45	$64.50
Purchase #5	$146.32	6.722%	$156.1556	$156.16	$156.15	$156.20
Purchase #6	$101.52	6.652%	$108.2731	$108.27	$108.25	$108.30
Purchase #7	$101.81	7.850%	$109.8021	$109.80	$109.80	$109.80
7 purchase totals =	$788.87		$842.8965	$842.90	$842.90	$843.00