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	$66.56	12.715%	$75.0231	$75.02	$75.00	$75.00
Purchase #2	$106.90	8.735%	$116.2377	$116.24	$116.25	$116.20
Purchase #3	$130.33	11.797%	$145.705	$145.71	$145.70	$145.70
Purchase #4	$189.85	10.405%	$209.6039	$209.60	$209.60	$209.60
Purchase #5	$57.40	4.307%	$59.8722	$59.87	$59.85	$59.90
Purchase #6	$212.30	13.552%	$241.0709	$241.07	$241.05	$241.10
Purchase #7	$161.53	4.234%	$168.3692	$168.37	$168.35	$168.40
7 purchase totals =	$924.87		$1,015.8820	$1,015.88	$1,015.80	$1,015.90