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	$159.73	4.110%	$166.2949	$166.29	$166.30	$166.30
Purchase #2	$24.76	12.720%	$27.9095	$27.91	$27.90	$27.90
Purchase #3	$90.29	5.648%	$95.3896	$95.39	$95.40	$95.40
Purchase #4	$10.44	10.339%	$11.5194	$11.52	$11.50	$11.50
Purchase #5	$100.65	11.791%	$112.5176	$112.52	$112.50	$112.50
Purchase #6	$36.93	6.707%	$39.4069	$39.41	$39.40	$39.40
Purchase #7	$155.53	7.427%	$167.0812	$167.08	$167.10	$167.10
7 purchase totals =	$578.33		$620.1191	$620.12	$620.10	$620.10