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	$17.72	13.392%	$20.0931	$20.09	$20.10	$20.10
Purchase #2	$249.78	8.318%	$270.5567	$270.56	$270.55	$270.60
Purchase #3	$141.73	7.158%	$151.875	$151.88	$151.90	$151.90
Purchase #4	$107.50	6.850%	$114.8638	$114.86	$114.85	$114.90
Purchase #5	$242.89	8.519%	$263.5818	$263.58	$263.60	$263.60
Purchase #6	$220.31	13.629%	$250.336	$250.34	$250.35	$250.30
Purchase #7	$160.30	4.442%	$167.4205	$167.42	$167.40	$167.40
7 purchase totals =	$1,140.23		$1,238.7269	$1,238.73	$1,238.75	$1,238.80