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	$37.98	13.527%	$43.1176	$43.12	$43.10	$43.10
Purchase #2	$169.76	11.209%	$188.7884	$188.79	$188.80	$188.80
Purchase #3	$90.85	12.204%	$101.9373	$101.94	$101.95	$101.90
Purchase #4	$235.89	7.799%	$254.2871	$254.29	$254.30	$254.30
Purchase #5	$107.87	11.315%	$120.0755	$120.08	$120.10	$120.10
Purchase #6	$13.86	5.356%	$14.6023	$14.60	$14.60	$14.60
Purchase #7	$211.89	3.597%	$219.5117	$219.51	$219.50	$219.50
7 purchase totals =	$868.10		$942.3199	$942.33	$942.35	$942.30