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	$86.55	3.330%	$89.4321	$89.43	$89.45	$89.40
Purchase #2	$64.44	12.832%	$72.7089	$72.71	$72.70	$72.70
Purchase #3	$127.74	9.789%	$140.2445	$140.24	$140.25	$140.20
Purchase #4	$33.79	11.693%	$37.7411	$37.74	$37.75	$37.70
Purchase #5	$223.35	9.697%	$245.0082	$245.01	$245.00	$245.00
Purchase #6	$155.68	13.405%	$176.5489	$176.55	$176.55	$176.50
Purchase #7	$120.51	9.726%	$132.2308	$132.23	$132.25	$132.20
7 purchase totals =	$812.06		$893.9145	$893.91	$893.95	$893.70