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	$72.35	3.478%	$74.8663	$74.87	$74.85	$74.90
Purchase #2	$32.79	7.211%	$35.1545	$35.15	$35.15	$35.20
Purchase #3	$161.97	10.441%	$178.8813	$178.88	$178.90	$178.90
Purchase #4	$131.51	11.467%	$146.5903	$146.59	$146.60	$146.60
Purchase #5	$66.60	5.607%	$70.3343	$70.33	$70.35	$70.30
Purchase #6	$42.59	8.498%	$46.2093	$46.21	$46.20	$46.20
Purchase #7	$106.55	8.142%	$115.2253	$115.23	$115.25	$115.20
7 purchase totals =	$614.36		$667.2613	$667.26	$667.30	$667.30