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	$80.89	5.420%	$85.2742	$85.27	$85.25	$85.30
Purchase #2	$167.86	10.687%	$185.7992	$185.80	$185.80	$185.80
Purchase #3	$243.60	9.728%	$267.2974	$267.30	$267.30	$267.30
Purchase #4	$78.74	3.812%	$81.7416	$81.74	$81.75	$81.70
Purchase #5	$119.55	8.745%	$130.0046	$130.00	$130.00	$130.00
Purchase #6	$110.72	11.535%	$123.4916	$123.49	$123.50	$123.50
Purchase #7	$58.87	10.869%	$65.2686	$65.27	$65.25	$65.30
7 purchase totals =	$860.23		$938.8772	$938.87	$938.85	$938.90