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	$115.75	11.556%	$129.1261	$129.13	$129.15	$129.10
Purchase #2	$88.68	13.751%	$100.8744	$100.87	$100.85	$100.90
Purchase #3	$198.35	9.333%	$216.862	$216.86	$216.85	$216.90
Purchase #4	$11.77	4.712%	$12.3246	$12.32	$12.30	$12.30
Purchase #5	$225.81	12.477%	$253.9843	$253.98	$254.00	$254.00
Purchase #6	$131.78	4.151%	$137.2502	$137.25	$137.25	$137.30
Purchase #7	$50.98	7.710%	$54.9106	$54.91	$54.90	$54.90
7 purchase totals =	$823.12		$905.3322	$905.32	$905.30	$905.40