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	$111.61	10.346%	$123.1572	$123.16	$123.15	$123.20
Purchase #2	$36.90	13.270%	$41.7966	$41.80	$41.80	$41.80
Purchase #3	$105.93	10.116%	$116.6459	$116.65	$116.65	$116.60
Purchase #4	$72.34	10.513%	$79.9451	$79.95	$79.95	$79.90
Purchase #5	$29.47	10.870%	$32.6734	$32.67	$32.65	$32.70
Purchase #6	$167.40	10.394%	$184.7996	$184.80	$184.80	$184.80
Purchase #7	$125.73	4.458%	$131.335	$131.34	$131.35	$131.30
7 purchase totals =	$649.38		$710.3528	$710.37	$710.35	$710.30