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	$85.73	5.864%	$90.7572	$90.76	$90.75	$90.80
Purchase #2	$152.34	8.537%	$165.3453	$165.35	$165.35	$165.30
Purchase #3	$73.67	9.797%	$80.8874	$80.89	$80.90	$80.90
Purchase #4	$146.67	12.381%	$164.8292	$164.83	$164.85	$164.80
Purchase #5	$157.87	5.843%	$167.0943	$167.09	$167.10	$167.10
Purchase #6	$213.35	5.258%	$224.5679	$224.57	$224.55	$224.60
Purchase #7	$149.28	5.573%	$157.5994	$157.60	$157.60	$157.60
7 purchase totals =	$978.91		$1,051.0807	$1,051.09	$1,051.10	$1,051.10