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	$172.73	4.142%	$179.8845	$179.88	$179.90	$179.90
Purchase #2	$61.37	6.612%	$65.4278	$65.43	$65.45	$65.40
Purchase #3	$241.44	7.449%	$259.4249	$259.42	$259.40	$259.40
Purchase #4	$147.79	9.715%	$162.1478	$162.15	$162.15	$162.10
Purchase #5	$204.75	6.530%	$218.1202	$218.12	$218.10	$218.10
Purchase #6	$42.81	10.376%	$47.252	$47.25	$47.25	$47.30
Purchase #7	$189.32	5.394%	$199.5319	$199.53	$199.55	$199.50
7 purchase totals =	$1,060.21		$1,131.7891	$1,131.78	$1,131.80	$1,131.70