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	$155.48	5.805%	$164.5056	$164.51	$164.50	$164.50
Purchase #2	$74.69	11.742%	$83.4601	$83.46	$83.45	$83.50
Purchase #3	$175.73	10.583%	$194.3275	$194.33	$194.35	$194.30
Purchase #4	$113.25	13.748%	$128.8196	$128.82	$128.80	$128.80
Purchase #5	$128.74	10.800%	$142.6439	$142.64	$142.65	$142.60
Purchase #6	$124.82	6.349%	$132.7448	$132.74	$132.75	$132.70
Purchase #7	$101.98	10.125%	$112.3055	$112.31	$112.30	$112.30
7 purchase totals =	$874.69		$958.8070	$958.81	$958.80	$958.70