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	$103.42	7.737%	$111.4216	$111.42	$111.40	$111.40
Purchase #2	$218.45	9.556%	$239.3251	$239.33	$239.35	$239.30
Purchase #3	$164.71	9.436%	$180.252	$180.25	$180.25	$180.30
Purchase #4	$180.50	10.145%	$198.8117	$198.81	$198.80	$198.80
Purchase #5	$166.32	8.171%	$179.91	$179.91	$179.90	$179.90
Purchase #6	$83.98	10.861%	$93.1011	$93.10	$93.10	$93.10
Purchase #7	$130.83	5.846%	$138.4783	$138.48	$138.50	$138.50
7 purchase totals =	$1,048.21		$1,141.2998	$1,141.30	$1,141.30	$1,141.30