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	$152.26	10.323%	$167.9778	$167.98	$168.00	$168.00
Purchase #2	$218.53	4.507%	$228.3791	$228.38	$228.40	$228.40
Purchase #3	$66.77	9.823%	$73.3288	$73.33	$73.35	$73.30
Purchase #4	$61.68	9.103%	$67.2947	$67.29	$67.30	$67.30
Purchase #5	$55.70	8.835%	$60.6211	$60.62	$60.60	$60.60
Purchase #6	$19.57	4.601%	$20.4704	$20.47	$20.45	$20.50
Purchase #7	$187.27	13.388%	$212.3417	$212.34	$212.35	$212.30
7 purchase totals =	$761.78		$830.4136	$830.41	$830.45	$830.40