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	$78.56	13.670%	$89.2992	$89.30	$89.30	$89.30
Purchase #2	$101.53	11.514%	$113.2202	$113.22	$113.20	$113.20
Purchase #3	$178.87	8.172%	$193.4873	$193.49	$193.50	$193.50
Purchase #4	$95.58	4.119%	$99.5169	$99.52	$99.50	$99.50
Purchase #5	$160.94	7.837%	$173.5529	$173.55	$173.55	$173.60
Purchase #6	$28.53	9.808%	$31.3282	$31.33	$31.35	$31.30
Purchase #7	$229.77	6.629%	$245.0015	$245.00	$245.00	$245.00
7 purchase totals =	$873.78		$945.4062	$945.41	$945.40	$945.40