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	$64.85	13.154%	$73.3804	$73.38	$73.40	$73.40
Purchase #2	$130.77	7.155%	$140.1266	$140.13	$140.15	$140.10
Purchase #3	$167.80	11.762%	$187.5366	$187.54	$187.55	$187.50
Purchase #4	$102.57	6.358%	$109.0914	$109.09	$109.10	$109.10
Purchase #5	$103.88	5.329%	$109.4158	$109.42	$109.40	$109.40
Purchase #6	$31.82	12.274%	$35.7256	$35.73	$35.75	$35.70
Purchase #7	$118.72	12.860%	$133.9874	$133.99	$134.00	$134.00
7 purchase totals =	$720.41		$789.2638	$789.28	$789.35	$789.20