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	$63.25	8.721%	$68.766	$68.77	$68.75	$68.80
Purchase #2	$17.74	13.736%	$20.1768	$20.18	$20.20	$20.20
Purchase #3	$87.27	3.233%	$90.0914	$90.09	$90.10	$90.10
Purchase #4	$103.25	11.216%	$114.8305	$114.83	$114.85	$114.80
Purchase #5	$28.71	9.339%	$31.3912	$31.39	$31.40	$31.40
Purchase #6	$34.67	7.171%	$37.1562	$37.16	$37.15	$37.20
Purchase #7	$136.28	3.544%	$141.1098	$141.11	$141.10	$141.10
7 purchase totals =	$471.17		$503.5219	$503.53	$503.55	$503.60