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	$79.80	11.195%	$88.7336	$88.73	$88.75	$88.70
Purchase #2	$151.65	10.848%	$168.101	$168.10	$168.10	$168.10
Purchase #3	$66.40	13.412%	$75.3056	$75.31	$75.30	$75.30
Purchase #4	$105.33	5.499%	$111.1221	$111.12	$111.10	$111.10
Purchase #5	$197.28	5.696%	$208.5171	$208.52	$208.50	$208.50
Purchase #6	$135.49	3.262%	$139.9097	$139.91	$139.90	$139.90
Purchase #7	$61.58	13.473%	$69.8767	$69.88	$69.90	$69.90
7 purchase totals =	$797.53		$861.5658	$861.57	$861.55	$861.50