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	$74.37	5.272%	$78.2908	$78.29	$78.30	$78.30
Purchase #2	$220.80	7.550%	$237.4704	$237.47	$237.45	$237.50
Purchase #3	$149.87	13.719%	$170.4307	$170.43	$170.45	$170.40
Purchase #4	$47.32	7.695%	$50.9613	$50.96	$50.95	$51.00
Purchase #5	$202.71	6.669%	$216.2287	$216.23	$216.25	$216.20
Purchase #6	$41.50	3.328%	$42.8811	$42.88	$42.90	$42.90
Purchase #7	$100.45	4.831%	$105.3027	$105.30	$105.30	$105.30
7 purchase totals =	$837.02		$901.5657	$901.56	$901.60	$901.60