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	$75.71	4.759%	$79.313	$79.31	$79.30	$79.30
Purchase #2	$249.40	11.484%	$278.0411	$278.04	$278.05	$278.00
Purchase #3	$102.28	9.154%	$111.6427	$111.64	$111.65	$111.60
Purchase #4	$190.98	10.656%	$211.3308	$211.33	$211.35	$211.30
Purchase #5	$114.89	13.569%	$130.4794	$130.48	$130.50	$130.50
Purchase #6	$122.47	7.175%	$131.2572	$131.26	$131.25	$131.30
Purchase #7	$174.43	7.406%	$187.3483	$187.35	$187.35	$187.30
7 purchase totals =	$1,030.16		$1,129.4125	$1,129.41	$1,129.45	$1,129.30