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	$32.38	9.721%	$35.5277	$35.53	$35.55	$35.50
Purchase #2	$187.76	13.379%	$212.8804	$212.88	$212.90	$212.90
Purchase #3	$160.79	4.138%	$167.4435	$167.44	$167.45	$167.40
Purchase #4	$146.53	9.549%	$160.5221	$160.52	$160.50	$160.50
Purchase #5	$206.52	10.598%	$228.407	$228.41	$228.40	$228.40
Purchase #6	$84.54	4.834%	$88.6267	$88.63	$88.65	$88.60
Purchase #7	$40.57	11.321%	$45.1629	$45.16	$45.15	$45.20
7 purchase totals =	$859.09		$938.5703	$938.57	$938.60	$938.50