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	$147.43	6.797%	$157.4508	$157.45	$157.45	$157.50
Purchase #2	$196.78	4.432%	$205.5013	$205.50	$205.50	$205.50
Purchase #3	$96.50	4.177%	$100.5308	$100.53	$100.55	$100.50
Purchase #4	$140.25	4.299%	$146.2793	$146.28	$146.30	$146.30
Purchase #5	$10.71	10.238%	$11.8065	$11.81	$11.80	$11.80
Purchase #6	$219.70	13.280%	$248.8762	$248.88	$248.90	$248.90
Purchase #7	$79.36	12.501%	$89.2808	$89.28	$89.30	$89.30
7 purchase totals =	$890.73		$959.7257	$959.73	$959.80	$959.80