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	$189.78	5.526%	$200.2672	$200.27	$200.25	$200.30
Purchase #2	$168.90	12.104%	$189.3437	$189.34	$189.35	$189.30
Purchase #3	$217.49	11.634%	$242.7928	$242.79	$242.80	$242.80
Purchase #4	$162.32	7.564%	$174.5979	$174.60	$174.60	$174.60
Purchase #5	$154.62	9.155%	$168.7755	$168.78	$168.80	$168.80
Purchase #6	$178.80	3.702%	$185.4192	$185.42	$185.40	$185.40
Purchase #7	$149.88	6.223%	$159.207	$159.21	$159.20	$159.20
7 purchase totals =	$1,221.79		$1,320.4033	$1,320.41	$1,320.40	$1,320.40