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	$67.95	12.705%	$76.583	$76.58	$76.60	$76.60
Purchase #2	$117.33	12.366%	$131.839	$131.84	$131.85	$131.80
Purchase #3	$63.65	5.804%	$67.3442	$67.34	$67.35	$67.30
Purchase #4	$104.65	5.589%	$110.4989	$110.50	$110.50	$110.50
Purchase #5	$165.79	11.589%	$185.0034	$185.00	$185.00	$185.00
Purchase #6	$122.80	10.159%	$135.2753	$135.28	$135.30	$135.30
Purchase #7	$116.91	12.817%	$131.8944	$131.89	$131.90	$131.90
7 purchase totals =	$759.08		$838.4382	$838.43	$838.50	$838.40