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	$52.69	9.728%	$57.8157	$57.82	$57.80	$57.80
Purchase #2	$101.67	3.420%	$105.1471	$105.15	$105.15	$105.10
Purchase #3	$190.85	11.756%	$213.2863	$213.29	$213.30	$213.30
Purchase #4	$160.29	4.403%	$167.3476	$167.35	$167.35	$167.30
Purchase #5	$173.71	4.782%	$182.0168	$182.02	$182.00	$182.00
Purchase #6	$220.46	3.599%	$228.3944	$228.39	$228.40	$228.40
Purchase #7	$31.30	13.473%	$35.517	$35.52	$35.50	$35.50
7 purchase totals =	$930.97		$989.5249	$989.54	$989.50	$989.40