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	$31.60	13.529%	$35.8752	$35.88	$35.90	$35.90
Purchase #2	$231.44	3.205%	$238.8577	$238.86	$238.85	$238.90
Purchase #3	$211.62	12.533%	$238.1423	$238.14	$238.15	$238.10
Purchase #4	$78.83	13.644%	$89.5856	$89.59	$89.60	$89.60
Purchase #5	$16.71	4.170%	$17.4068	$17.41	$17.40	$17.40
Purchase #6	$215.58	13.246%	$244.1357	$244.14	$244.15	$244.10
Purchase #7	$188.72	12.516%	$212.3402	$212.34	$212.35	$212.30
7 purchase totals =	$974.50		$1,076.3435	$1,076.36	$1,076.40	$1,076.30